77a045e902
-Reworked how meshes are treated by importer by using EditorSceneImporterMesh and EditorSceneImporterMeshNode. Instead of Mesh and MeshInstance, this allows more efficient processing of meshes before they are actually registered in the RenderingServer. -Integrated MeshOptimizer -Reworked internals of SurfaceTool to use arrays, making it more performant and easy to run optimizatons on.
753 lines
22 KiB
C++
753 lines
22 KiB
C++
// This file is part of meshoptimizer library; see meshoptimizer.h for version/license details
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#include "meshoptimizer.h"
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#include <assert.h>
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#include <string.h>
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#ifndef TRACE
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#define TRACE 0
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#endif
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#if TRACE
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#include <stdio.h>
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#endif
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// This work is based on:
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// Fabian Giesen. Simple lossless index buffer compression & follow-up. 2013
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// Conor Stokes. Vertex Cache Optimised Index Buffer Compression. 2014
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namespace meshopt
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{
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const unsigned char kIndexHeader = 0xe0;
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const unsigned char kSequenceHeader = 0xd0;
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static int gEncodeIndexVersion = 0;
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typedef unsigned int VertexFifo[16];
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typedef unsigned int EdgeFifo[16][2];
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static const unsigned int kTriangleIndexOrder[3][3] = {
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{0, 1, 2},
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{1, 2, 0},
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{2, 0, 1},
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};
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static const unsigned char kCodeAuxEncodingTable[16] = {
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0x00, 0x76, 0x87, 0x56, 0x67, 0x78, 0xa9, 0x86, 0x65, 0x89, 0x68, 0x98, 0x01, 0x69,
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0, 0, // last two entries aren't used for encoding
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};
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static int rotateTriangle(unsigned int a, unsigned int b, unsigned int c, unsigned int next)
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{
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(void)a;
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return (b == next) ? 1 : (c == next) ? 2 : 0;
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}
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static int getEdgeFifo(EdgeFifo fifo, unsigned int a, unsigned int b, unsigned int c, size_t offset)
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{
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for (int i = 0; i < 16; ++i)
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{
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size_t index = (offset - 1 - i) & 15;
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unsigned int e0 = fifo[index][0];
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unsigned int e1 = fifo[index][1];
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if (e0 == a && e1 == b)
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return (i << 2) | 0;
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if (e0 == b && e1 == c)
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return (i << 2) | 1;
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if (e0 == c && e1 == a)
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return (i << 2) | 2;
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}
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return -1;
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}
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static void pushEdgeFifo(EdgeFifo fifo, unsigned int a, unsigned int b, size_t& offset)
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{
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fifo[offset][0] = a;
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fifo[offset][1] = b;
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offset = (offset + 1) & 15;
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}
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static int getVertexFifo(VertexFifo fifo, unsigned int v, size_t offset)
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{
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for (int i = 0; i < 16; ++i)
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{
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size_t index = (offset - 1 - i) & 15;
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if (fifo[index] == v)
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return i;
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}
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return -1;
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}
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static void pushVertexFifo(VertexFifo fifo, unsigned int v, size_t& offset, int cond = 1)
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{
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fifo[offset] = v;
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offset = (offset + cond) & 15;
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}
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static void encodeVByte(unsigned char*& data, unsigned int v)
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{
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// encode 32-bit value in up to 5 7-bit groups
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do
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{
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*data++ = (v & 127) | (v > 127 ? 128 : 0);
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v >>= 7;
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} while (v);
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}
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static unsigned int decodeVByte(const unsigned char*& data)
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{
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unsigned char lead = *data++;
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// fast path: single byte
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if (lead < 128)
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return lead;
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// slow path: up to 4 extra bytes
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// note that this loop always terminates, which is important for malformed data
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unsigned int result = lead & 127;
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unsigned int shift = 7;
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for (int i = 0; i < 4; ++i)
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{
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unsigned char group = *data++;
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result |= (group & 127) << shift;
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shift += 7;
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if (group < 128)
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break;
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}
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return result;
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}
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static void encodeIndex(unsigned char*& data, unsigned int index, unsigned int last)
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{
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unsigned int d = index - last;
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unsigned int v = (d << 1) ^ (int(d) >> 31);
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encodeVByte(data, v);
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}
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static unsigned int decodeIndex(const unsigned char*& data, unsigned int last)
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{
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unsigned int v = decodeVByte(data);
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unsigned int d = (v >> 1) ^ -int(v & 1);
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return last + d;
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}
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static int getCodeAuxIndex(unsigned char v, const unsigned char* table)
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{
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for (int i = 0; i < 16; ++i)
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if (table[i] == v)
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return i;
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return -1;
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}
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static void writeTriangle(void* destination, size_t offset, size_t index_size, unsigned int a, unsigned int b, unsigned int c)
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{
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if (index_size == 2)
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{
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static_cast<unsigned short*>(destination)[offset + 0] = (unsigned short)(a);
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static_cast<unsigned short*>(destination)[offset + 1] = (unsigned short)(b);
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static_cast<unsigned short*>(destination)[offset + 2] = (unsigned short)(c);
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}
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else
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{
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static_cast<unsigned int*>(destination)[offset + 0] = a;
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static_cast<unsigned int*>(destination)[offset + 1] = b;
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static_cast<unsigned int*>(destination)[offset + 2] = c;
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}
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}
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#if TRACE
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static size_t sortTop16(unsigned char dest[16], size_t stats[256])
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{
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size_t destsize = 0;
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for (size_t i = 0; i < 256; ++i)
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{
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size_t j = 0;
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for (; j < destsize; ++j)
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{
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if (stats[i] >= stats[dest[j]])
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{
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if (destsize < 16)
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destsize++;
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memmove(&dest[j + 1], &dest[j], destsize - 1 - j);
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dest[j] = (unsigned char)i;
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break;
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}
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}
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if (j == destsize && destsize < 16)
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{
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dest[destsize] = (unsigned char)i;
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destsize++;
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}
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}
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return destsize;
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}
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#endif
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} // namespace meshopt
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size_t meshopt_encodeIndexBuffer(unsigned char* buffer, size_t buffer_size, const unsigned int* indices, size_t index_count)
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{
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using namespace meshopt;
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assert(index_count % 3 == 0);
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#if TRACE
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size_t codestats[256] = {};
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size_t codeauxstats[256] = {};
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#endif
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// the minimum valid encoding is header, 1 byte per triangle and a 16-byte codeaux table
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if (buffer_size < 1 + index_count / 3 + 16)
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return 0;
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int version = gEncodeIndexVersion;
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buffer[0] = (unsigned char)(kIndexHeader | version);
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EdgeFifo edgefifo;
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memset(edgefifo, -1, sizeof(edgefifo));
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VertexFifo vertexfifo;
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memset(vertexfifo, -1, sizeof(vertexfifo));
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size_t edgefifooffset = 0;
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size_t vertexfifooffset = 0;
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unsigned int next = 0;
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unsigned int last = 0;
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unsigned char* code = buffer + 1;
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unsigned char* data = code + index_count / 3;
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unsigned char* data_safe_end = buffer + buffer_size - 16;
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int fecmax = version >= 1 ? 13 : 15;
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// use static encoding table; it's possible to pack the result and then build an optimal table and repack
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// for now we keep it simple and use the table that has been generated based on symbol frequency on a training mesh set
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const unsigned char* codeaux_table = kCodeAuxEncodingTable;
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for (size_t i = 0; i < index_count; i += 3)
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{
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// make sure we have enough space to write a triangle
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// each triangle writes at most 16 bytes: 1b for codeaux and 5b for each free index
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// after this we can be sure we can write without extra bounds checks
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if (data > data_safe_end)
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return 0;
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int fer = getEdgeFifo(edgefifo, indices[i + 0], indices[i + 1], indices[i + 2], edgefifooffset);
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if (fer >= 0 && (fer >> 2) < 15)
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{
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const unsigned int* order = kTriangleIndexOrder[fer & 3];
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unsigned int a = indices[i + order[0]], b = indices[i + order[1]], c = indices[i + order[2]];
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// encode edge index and vertex fifo index, next or free index
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int fe = fer >> 2;
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int fc = getVertexFifo(vertexfifo, c, vertexfifooffset);
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int fec = (fc >= 1 && fc < fecmax) ? fc : (c == next) ? (next++, 0) : 15;
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if (fec == 15 && version >= 1)
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{
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// encode last-1 and last+1 to optimize strip-like sequences
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if (c + 1 == last)
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fec = 13, last = c;
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if (c == last + 1)
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fec = 14, last = c;
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}
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*code++ = (unsigned char)((fe << 4) | fec);
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#if TRACE
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codestats[code[-1]]++;
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#endif
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// note that we need to update the last index since free indices are delta-encoded
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if (fec == 15)
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encodeIndex(data, c, last), last = c;
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// we only need to push third vertex since first two are likely already in the vertex fifo
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if (fec == 0 || fec >= fecmax)
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pushVertexFifo(vertexfifo, c, vertexfifooffset);
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// we only need to push two new edges to edge fifo since the third one is already there
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pushEdgeFifo(edgefifo, c, b, edgefifooffset);
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pushEdgeFifo(edgefifo, a, c, edgefifooffset);
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}
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else
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{
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int rotation = rotateTriangle(indices[i + 0], indices[i + 1], indices[i + 2], next);
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const unsigned int* order = kTriangleIndexOrder[rotation];
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unsigned int a = indices[i + order[0]], b = indices[i + order[1]], c = indices[i + order[2]];
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// if a/b/c are 0/1/2, we emit a reset code
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bool reset = false;
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if (a == 0 && b == 1 && c == 2 && next > 0 && version >= 1)
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{
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reset = true;
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next = 0;
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// reset vertex fifo to make sure we don't accidentally reference vertices from that in the future
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// this makes sure next continues to get incremented instead of being stuck
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memset(vertexfifo, -1, sizeof(vertexfifo));
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}
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int fb = getVertexFifo(vertexfifo, b, vertexfifooffset);
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int fc = getVertexFifo(vertexfifo, c, vertexfifooffset);
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// after rotation, a is almost always equal to next, so we don't waste bits on FIFO encoding for a
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int fea = (a == next) ? (next++, 0) : 15;
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int feb = (fb >= 0 && fb < 14) ? (fb + 1) : (b == next) ? (next++, 0) : 15;
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int fec = (fc >= 0 && fc < 14) ? (fc + 1) : (c == next) ? (next++, 0) : 15;
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// we encode feb & fec in 4 bits using a table if possible, and as a full byte otherwise
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unsigned char codeaux = (unsigned char)((feb << 4) | fec);
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int codeauxindex = getCodeAuxIndex(codeaux, codeaux_table);
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// <14 encodes an index into codeaux table, 14 encodes fea=0, 15 encodes fea=15
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if (fea == 0 && codeauxindex >= 0 && codeauxindex < 14 && !reset)
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{
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*code++ = (unsigned char)((15 << 4) | codeauxindex);
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}
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else
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{
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*code++ = (unsigned char)((15 << 4) | 14 | fea);
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*data++ = codeaux;
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}
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#if TRACE
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codestats[code[-1]]++;
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codeauxstats[codeaux]++;
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#endif
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// note that we need to update the last index since free indices are delta-encoded
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if (fea == 15)
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encodeIndex(data, a, last), last = a;
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if (feb == 15)
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encodeIndex(data, b, last), last = b;
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if (fec == 15)
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encodeIndex(data, c, last), last = c;
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// only push vertices that weren't already in fifo
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if (fea == 0 || fea == 15)
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pushVertexFifo(vertexfifo, a, vertexfifooffset);
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if (feb == 0 || feb == 15)
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pushVertexFifo(vertexfifo, b, vertexfifooffset);
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if (fec == 0 || fec == 15)
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pushVertexFifo(vertexfifo, c, vertexfifooffset);
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// all three edges aren't in the fifo; pushing all of them is important so that we can match them for later triangles
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pushEdgeFifo(edgefifo, b, a, edgefifooffset);
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pushEdgeFifo(edgefifo, c, b, edgefifooffset);
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pushEdgeFifo(edgefifo, a, c, edgefifooffset);
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}
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}
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// make sure we have enough space to write codeaux table
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if (data > data_safe_end)
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return 0;
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// add codeaux encoding table to the end of the stream; this is used for decoding codeaux *and* as padding
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// we need padding for decoding to be able to assume that each triangle is encoded as <= 16 bytes of extra data
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// this is enough space for aux byte + 5 bytes per varint index which is the absolute worst case for any input
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for (size_t i = 0; i < 16; ++i)
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{
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// decoder assumes that table entries never refer to separately encoded indices
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assert((codeaux_table[i] & 0xf) != 0xf && (codeaux_table[i] >> 4) != 0xf);
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*data++ = codeaux_table[i];
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}
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// since we encode restarts as codeaux without a table reference, we need to make sure 00 is encoded as a table reference
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assert(codeaux_table[0] == 0);
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assert(data >= buffer + index_count / 3 + 16);
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assert(data <= buffer + buffer_size);
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#if TRACE
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unsigned char codetop[16], codeauxtop[16];
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size_t codetopsize = sortTop16(codetop, codestats);
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size_t codeauxtopsize = sortTop16(codeauxtop, codeauxstats);
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size_t sumcode = 0, sumcodeaux = 0;
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for (size_t i = 0; i < 256; ++i)
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sumcode += codestats[i], sumcodeaux += codeauxstats[i];
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size_t acccode = 0, acccodeaux = 0;
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printf("code\t\t\t\t\tcodeaux\n");
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for (size_t i = 0; i < codetopsize && i < codeauxtopsize; ++i)
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{
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acccode += codestats[codetop[i]];
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acccodeaux += codeauxstats[codeauxtop[i]];
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printf("%2d: %02x = %d (%.1f%% ..%.1f%%)\t\t%2d: %02x = %d (%.1f%% ..%.1f%%)\n",
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int(i), codetop[i], int(codestats[codetop[i]]), double(codestats[codetop[i]]) / double(sumcode) * 100, double(acccode) / double(sumcode) * 100,
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int(i), codeauxtop[i], int(codeauxstats[codeauxtop[i]]), double(codeauxstats[codeauxtop[i]]) / double(sumcodeaux) * 100, double(acccodeaux) / double(sumcodeaux) * 100);
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}
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#endif
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return data - buffer;
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}
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size_t meshopt_encodeIndexBufferBound(size_t index_count, size_t vertex_count)
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{
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assert(index_count % 3 == 0);
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// compute number of bits required for each index
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unsigned int vertex_bits = 1;
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while (vertex_bits < 32 && vertex_count > size_t(1) << vertex_bits)
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vertex_bits++;
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// worst-case encoding is 2 header bytes + 3 varint-7 encoded index deltas
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unsigned int vertex_groups = (vertex_bits + 1 + 6) / 7;
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return 1 + (index_count / 3) * (2 + 3 * vertex_groups) + 16;
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}
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void meshopt_encodeIndexVersion(int version)
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{
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assert(unsigned(version) <= 1);
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meshopt::gEncodeIndexVersion = version;
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}
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int meshopt_decodeIndexBuffer(void* destination, size_t index_count, size_t index_size, const unsigned char* buffer, size_t buffer_size)
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{
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using namespace meshopt;
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assert(index_count % 3 == 0);
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assert(index_size == 2 || index_size == 4);
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// the minimum valid encoding is header, 1 byte per triangle and a 16-byte codeaux table
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if (buffer_size < 1 + index_count / 3 + 16)
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return -2;
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if ((buffer[0] & 0xf0) != kIndexHeader)
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return -1;
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int version = buffer[0] & 0x0f;
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if (version > 1)
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return -1;
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EdgeFifo edgefifo;
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memset(edgefifo, -1, sizeof(edgefifo));
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VertexFifo vertexfifo;
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memset(vertexfifo, -1, sizeof(vertexfifo));
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size_t edgefifooffset = 0;
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size_t vertexfifooffset = 0;
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unsigned int next = 0;
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unsigned int last = 0;
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int fecmax = version >= 1 ? 13 : 15;
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// since we store 16-byte codeaux table at the end, triangle data has to begin before data_safe_end
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const unsigned char* code = buffer + 1;
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const unsigned char* data = code + index_count / 3;
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const unsigned char* data_safe_end = buffer + buffer_size - 16;
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const unsigned char* codeaux_table = data_safe_end;
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for (size_t i = 0; i < index_count; i += 3)
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{
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// make sure we have enough data to read for a triangle
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// each triangle reads at most 16 bytes of data: 1b for codeaux and 5b for each free index
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// after this we can be sure we can read without extra bounds checks
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if (data > data_safe_end)
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return -2;
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unsigned char codetri = *code++;
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if (codetri < 0xf0)
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{
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int fe = codetri >> 4;
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// fifo reads are wrapped around 16 entry buffer
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unsigned int a = edgefifo[(edgefifooffset - 1 - fe) & 15][0];
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unsigned int b = edgefifo[(edgefifooffset - 1 - fe) & 15][1];
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int fec = codetri & 15;
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// note: this is the most common path in the entire decoder
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// inside this if we try to stay branchless (by using cmov/etc.) since these aren't predictable
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if (fec < fecmax)
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{
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// fifo reads are wrapped around 16 entry buffer
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unsigned int cf = vertexfifo[(vertexfifooffset - 1 - fec) & 15];
|
|
unsigned int c = (fec == 0) ? next : cf;
|
|
|
|
int fec0 = fec == 0;
|
|
next += fec0;
|
|
|
|
// output triangle
|
|
writeTriangle(destination, i, index_size, a, b, c);
|
|
|
|
// push vertex/edge fifo must match the encoding step *exactly* otherwise the data will not be decoded correctly
|
|
pushVertexFifo(vertexfifo, c, vertexfifooffset, fec0);
|
|
|
|
pushEdgeFifo(edgefifo, c, b, edgefifooffset);
|
|
pushEdgeFifo(edgefifo, a, c, edgefifooffset);
|
|
}
|
|
else
|
|
{
|
|
unsigned int c = 0;
|
|
|
|
// fec - (fec ^ 3) decodes 13, 14 into -1, 1
|
|
// note that we need to update the last index since free indices are delta-encoded
|
|
last = c = (fec != 15) ? last + (fec - (fec ^ 3)) : decodeIndex(data, last);
|
|
|
|
// output triangle
|
|
writeTriangle(destination, i, index_size, a, b, c);
|
|
|
|
// push vertex/edge fifo must match the encoding step *exactly* otherwise the data will not be decoded correctly
|
|
pushVertexFifo(vertexfifo, c, vertexfifooffset);
|
|
|
|
pushEdgeFifo(edgefifo, c, b, edgefifooffset);
|
|
pushEdgeFifo(edgefifo, a, c, edgefifooffset);
|
|
}
|
|
}
|
|
else
|
|
{
|
|
// fast path: read codeaux from the table
|
|
if (codetri < 0xfe)
|
|
{
|
|
unsigned char codeaux = codeaux_table[codetri & 15];
|
|
|
|
// note: table can't contain feb/fec=15
|
|
int feb = codeaux >> 4;
|
|
int fec = codeaux & 15;
|
|
|
|
// fifo reads are wrapped around 16 entry buffer
|
|
// also note that we increment next for all three vertices before decoding indices - this matches encoder behavior
|
|
unsigned int a = next++;
|
|
|
|
unsigned int bf = vertexfifo[(vertexfifooffset - feb) & 15];
|
|
unsigned int b = (feb == 0) ? next : bf;
|
|
|
|
int feb0 = feb == 0;
|
|
next += feb0;
|
|
|
|
unsigned int cf = vertexfifo[(vertexfifooffset - fec) & 15];
|
|
unsigned int c = (fec == 0) ? next : cf;
|
|
|
|
int fec0 = fec == 0;
|
|
next += fec0;
|
|
|
|
// output triangle
|
|
writeTriangle(destination, i, index_size, a, b, c);
|
|
|
|
// push vertex/edge fifo must match the encoding step *exactly* otherwise the data will not be decoded correctly
|
|
pushVertexFifo(vertexfifo, a, vertexfifooffset);
|
|
pushVertexFifo(vertexfifo, b, vertexfifooffset, feb0);
|
|
pushVertexFifo(vertexfifo, c, vertexfifooffset, fec0);
|
|
|
|
pushEdgeFifo(edgefifo, b, a, edgefifooffset);
|
|
pushEdgeFifo(edgefifo, c, b, edgefifooffset);
|
|
pushEdgeFifo(edgefifo, a, c, edgefifooffset);
|
|
}
|
|
else
|
|
{
|
|
// slow path: read a full byte for codeaux instead of using a table lookup
|
|
unsigned char codeaux = *data++;
|
|
|
|
int fea = codetri == 0xfe ? 0 : 15;
|
|
int feb = codeaux >> 4;
|
|
int fec = codeaux & 15;
|
|
|
|
// reset: codeaux is 0 but encoded as not-a-table
|
|
if (codeaux == 0)
|
|
next = 0;
|
|
|
|
// fifo reads are wrapped around 16 entry buffer
|
|
// also note that we increment next for all three vertices before decoding indices - this matches encoder behavior
|
|
unsigned int a = (fea == 0) ? next++ : 0;
|
|
unsigned int b = (feb == 0) ? next++ : vertexfifo[(vertexfifooffset - feb) & 15];
|
|
unsigned int c = (fec == 0) ? next++ : vertexfifo[(vertexfifooffset - fec) & 15];
|
|
|
|
// note that we need to update the last index since free indices are delta-encoded
|
|
if (fea == 15)
|
|
last = a = decodeIndex(data, last);
|
|
|
|
if (feb == 15)
|
|
last = b = decodeIndex(data, last);
|
|
|
|
if (fec == 15)
|
|
last = c = decodeIndex(data, last);
|
|
|
|
// output triangle
|
|
writeTriangle(destination, i, index_size, a, b, c);
|
|
|
|
// push vertex/edge fifo must match the encoding step *exactly* otherwise the data will not be decoded correctly
|
|
pushVertexFifo(vertexfifo, a, vertexfifooffset);
|
|
pushVertexFifo(vertexfifo, b, vertexfifooffset, (feb == 0) | (feb == 15));
|
|
pushVertexFifo(vertexfifo, c, vertexfifooffset, (fec == 0) | (fec == 15));
|
|
|
|
pushEdgeFifo(edgefifo, b, a, edgefifooffset);
|
|
pushEdgeFifo(edgefifo, c, b, edgefifooffset);
|
|
pushEdgeFifo(edgefifo, a, c, edgefifooffset);
|
|
}
|
|
}
|
|
}
|
|
|
|
// we should've read all data bytes and stopped at the boundary between data and codeaux table
|
|
if (data != data_safe_end)
|
|
return -3;
|
|
|
|
return 0;
|
|
}
|
|
|
|
size_t meshopt_encodeIndexSequence(unsigned char* buffer, size_t buffer_size, const unsigned int* indices, size_t index_count)
|
|
{
|
|
using namespace meshopt;
|
|
|
|
// the minimum valid encoding is header, 1 byte per index and a 4-byte tail
|
|
if (buffer_size < 1 + index_count + 4)
|
|
return 0;
|
|
|
|
int version = gEncodeIndexVersion;
|
|
|
|
buffer[0] = (unsigned char)(kSequenceHeader | version);
|
|
|
|
unsigned int last[2] = {};
|
|
unsigned int current = 0;
|
|
|
|
unsigned char* data = buffer + 1;
|
|
unsigned char* data_safe_end = buffer + buffer_size - 4;
|
|
|
|
for (size_t i = 0; i < index_count; ++i)
|
|
{
|
|
// make sure we have enough data to write
|
|
// each index writes at most 5 bytes of data; there's a 4 byte tail after data_safe_end
|
|
// after this we can be sure we can write without extra bounds checks
|
|
if (data >= data_safe_end)
|
|
return 0;
|
|
|
|
unsigned int index = indices[i];
|
|
|
|
// this is a heuristic that switches between baselines when the delta grows too large
|
|
// we want the encoded delta to fit into one byte (7 bits), but 2 bits are used for sign and baseline index
|
|
// for now we immediately switch the baseline when delta grows too large - this can be adjusted arbitrarily
|
|
int cd = int(index - last[current]);
|
|
current ^= ((cd < 0 ? -cd : cd) >= 30);
|
|
|
|
// encode delta from the last index
|
|
unsigned int d = index - last[current];
|
|
unsigned int v = (d << 1) ^ (int(d) >> 31);
|
|
|
|
// note: low bit encodes the index of the last baseline which will be used for reconstruction
|
|
encodeVByte(data, (v << 1) | current);
|
|
|
|
// update last for the next iteration that uses it
|
|
last[current] = index;
|
|
}
|
|
|
|
// make sure we have enough space to write tail
|
|
if (data > data_safe_end)
|
|
return 0;
|
|
|
|
for (int k = 0; k < 4; ++k)
|
|
*data++ = 0;
|
|
|
|
return data - buffer;
|
|
}
|
|
|
|
size_t meshopt_encodeIndexSequenceBound(size_t index_count, size_t vertex_count)
|
|
{
|
|
// compute number of bits required for each index
|
|
unsigned int vertex_bits = 1;
|
|
|
|
while (vertex_bits < 32 && vertex_count > size_t(1) << vertex_bits)
|
|
vertex_bits++;
|
|
|
|
// worst-case encoding is 1 varint-7 encoded index delta for a K bit value and an extra bit
|
|
unsigned int vertex_groups = (vertex_bits + 1 + 1 + 6) / 7;
|
|
|
|
return 1 + index_count * vertex_groups + 4;
|
|
}
|
|
|
|
int meshopt_decodeIndexSequence(void* destination, size_t index_count, size_t index_size, const unsigned char* buffer, size_t buffer_size)
|
|
{
|
|
using namespace meshopt;
|
|
|
|
// the minimum valid encoding is header, 1 byte per index and a 4-byte tail
|
|
if (buffer_size < 1 + index_count + 4)
|
|
return -2;
|
|
|
|
if ((buffer[0] & 0xf0) != kSequenceHeader)
|
|
return -1;
|
|
|
|
int version = buffer[0] & 0x0f;
|
|
if (version > 1)
|
|
return -1;
|
|
|
|
const unsigned char* data = buffer + 1;
|
|
const unsigned char* data_safe_end = buffer + buffer_size - 4;
|
|
|
|
unsigned int last[2] = {};
|
|
|
|
for (size_t i = 0; i < index_count; ++i)
|
|
{
|
|
// make sure we have enough data to read
|
|
// each index reads at most 5 bytes of data; there's a 4 byte tail after data_safe_end
|
|
// after this we can be sure we can read without extra bounds checks
|
|
if (data >= data_safe_end)
|
|
return -2;
|
|
|
|
unsigned int v = decodeVByte(data);
|
|
|
|
// decode the index of the last baseline
|
|
unsigned int current = v & 1;
|
|
v >>= 1;
|
|
|
|
// reconstruct index as a delta
|
|
unsigned int d = (v >> 1) ^ -int(v & 1);
|
|
unsigned int index = last[current] + d;
|
|
|
|
// update last for the next iteration that uses it
|
|
last[current] = index;
|
|
|
|
if (index_size == 2)
|
|
{
|
|
static_cast<unsigned short*>(destination)[i] = (unsigned short)(index);
|
|
}
|
|
else
|
|
{
|
|
static_cast<unsigned int*>(destination)[i] = index;
|
|
}
|
|
}
|
|
|
|
// we should've read all data bytes and stopped at the boundary between data and tail
|
|
if (data != data_safe_end)
|
|
return -3;
|
|
|
|
return 0;
|
|
}
|