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ImHash: Moved crc32 table out of the function so it can be shared, also avoid cases were compiler tries to makes its initialization thread-safe.

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omar 2019-01-21 15:13:54 +01:00
parent 1e4cf67a53
commit f994b8aab8
1 changed files with 25 additions and 13 deletions
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38
imgui.cpp
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@ -1433,28 +1433,39 @@ int ImFormatStringV(char* buf, size_t buf_size, const char* fmt, va_list args)
} }
#endif // #ifdef IMGUI_DISABLE_FORMAT_STRING_FUNCTIONS #endif // #ifdef IMGUI_DISABLE_FORMAT_STRING_FUNCTIONS
// CRC32 needs a 1KB lookup table (not cache friendly)
// Although the code to generate the table is simple and shorter than the table itself, using a const table allows us to easily:
// - avoid an unnecessary branch/memory tap, - keep the ImHash() function usable by static constructors, - make it thread-safe.
static const ImU32 GCrc32LookupTable[256] =
{
0x00000000,0x77073096,0xEE0E612C,0x990951BA,0x076DC419,0x706AF48F,0xE963A535,0x9E6495A3,0x0EDB8832,0x79DCB8A4,0xE0D5E91E,0x97D2D988,0x09B64C2B,0x7EB17CBD,0xE7B82D07,0x90BF1D91,
0x1DB71064,0x6AB020F2,0xF3B97148,0x84BE41DE,0x1ADAD47D,0x6DDDE4EB,0xF4D4B551,0x83D385C7,0x136C9856,0x646BA8C0,0xFD62F97A,0x8A65C9EC,0x14015C4F,0x63066CD9,0xFA0F3D63,0x8D080DF5,
0x3B6E20C8,0x4C69105E,0xD56041E4,0xA2677172,0x3C03E4D1,0x4B04D447,0xD20D85FD,0xA50AB56B,0x35B5A8FA,0x42B2986C,0xDBBBC9D6,0xACBCF940,0x32D86CE3,0x45DF5C75,0xDCD60DCF,0xABD13D59,
0x26D930AC,0x51DE003A,0xC8D75180,0xBFD06116,0x21B4F4B5,0x56B3C423,0xCFBA9599,0xB8BDA50F,0x2802B89E,0x5F058808,0xC60CD9B2,0xB10BE924,0x2F6F7C87,0x58684C11,0xC1611DAB,0xB6662D3D,
0x76DC4190,0x01DB7106,0x98D220BC,0xEFD5102A,0x71B18589,0x06B6B51F,0x9FBFE4A5,0xE8B8D433,0x7807C9A2,0x0F00F934,0x9609A88E,0xE10E9818,0x7F6A0DBB,0x086D3D2D,0x91646C97,0xE6635C01,
0x6B6B51F4,0x1C6C6162,0x856530D8,0xF262004E,0x6C0695ED,0x1B01A57B,0x8208F4C1,0xF50FC457,0x65B0D9C6,0x12B7E950,0x8BBEB8EA,0xFCB9887C,0x62DD1DDF,0x15DA2D49,0x8CD37CF3,0xFBD44C65,
0x4DB26158,0x3AB551CE,0xA3BC0074,0xD4BB30E2,0x4ADFA541,0x3DD895D7,0xA4D1C46D,0xD3D6F4FB,0x4369E96A,0x346ED9FC,0xAD678846,0xDA60B8D0,0x44042D73,0x33031DE5,0xAA0A4C5F,0xDD0D7CC9,
0x5005713C,0x270241AA,0xBE0B1010,0xC90C2086,0x5768B525,0x206F85B3,0xB966D409,0xCE61E49F,0x5EDEF90E,0x29D9C998,0xB0D09822,0xC7D7A8B4,0x59B33D17,0x2EB40D81,0xB7BD5C3B,0xC0BA6CAD,
0xEDB88320,0x9ABFB3B6,0x03B6E20C,0x74B1D29A,0xEAD54739,0x9DD277AF,0x04DB2615,0x73DC1683,0xE3630B12,0x94643B84,0x0D6D6A3E,0x7A6A5AA8,0xE40ECF0B,0x9309FF9D,0x0A00AE27,0x7D079EB1,
0xF00F9344,0x8708A3D2,0x1E01F268,0x6906C2FE,0xF762575D,0x806567CB,0x196C3671,0x6E6B06E7,0xFED41B76,0x89D32BE0,0x10DA7A5A,0x67DD4ACC,0xF9B9DF6F,0x8EBEEFF9,0x17B7BE43,0x60B08ED5,
0xD6D6A3E8,0xA1D1937E,0x38D8C2C4,0x4FDFF252,0xD1BB67F1,0xA6BC5767,0x3FB506DD,0x48B2364B,0xD80D2BDA,0xAF0A1B4C,0x36034AF6,0x41047A60,0xDF60EFC3,0xA867DF55,0x316E8EEF,0x4669BE79,
0xCB61B38C,0xBC66831A,0x256FD2A0,0x5268E236,0xCC0C7795,0xBB0B4703,0x220216B9,0x5505262F,0xC5BA3BBE,0xB2BD0B28,0x2BB45A92,0x5CB36A04,0xC2D7FFA7,0xB5D0CF31,0x2CD99E8B,0x5BDEAE1D,
0x9B64C2B0,0xEC63F226,0x756AA39C,0x026D930A,0x9C0906A9,0xEB0E363F,0x72076785,0x05005713,0x95BF4A82,0xE2B87A14,0x7BB12BAE,0x0CB61B38,0x92D28E9B,0xE5D5BE0D,0x7CDCEFB7,0x0BDBDF21,
0x86D3D2D4,0xF1D4E242,0x68DDB3F8,0x1FDA836E,0x81BE16CD,0xF6B9265B,0x6FB077E1,0x18B74777,0x88085AE6,0xFF0F6A70,0x66063BCA,0x11010B5C,0x8F659EFF,0xF862AE69,0x616BFFD3,0x166CCF45,
0xA00AE278,0xD70DD2EE,0x4E048354,0x3903B3C2,0xA7672661,0xD06016F7,0x4969474D,0x3E6E77DB,0xAED16A4A,0xD9D65ADC,0x40DF0B66,0x37D83BF0,0xA9BCAE53,0xDEBB9EC5,0x47B2CF7F,0x30B5FFE9,
0xBDBDF21C,0xCABAC28A,0x53B39330,0x24B4A3A6,0xBAD03605,0xCDD70693,0x54DE5729,0x23D967BF,0xB3667A2E,0xC4614AB8,0x5D681B02,0x2A6F2B94,0xB40BBE37,0xC30C8EA1,0x5A05DF1B,0x2D02EF8D,
};
// Pass data_size == 0 for zero-terminated strings, data_size > 0 for non-string data. // Pass data_size == 0 for zero-terminated strings, data_size > 0 for non-string data.
// Pay attention that data_size==0 will yield different results than passing strlen(data) because the zero-terminated codepath handles ###. // Pay attention that data_size==0 will yield different results than passing strlen(data) because the zero-terminated codepath handles ###.
// This should technically be split into two distinct functions (ImHashData/ImHashStr), perhaps once we remove the silly static variable. // This should technically be split into two distinct functions (ImHashData/ImHashStr), perhaps once we remove the silly static variable.
// FIXME-OPT: Replace with e.g. FNV1a hash? CRC32 pretty much randomly access 1KB. Need to do proper measurements. // FIXME-OPT: Replace with e.g. FNV1a hash? CRC32 pretty much randomly access 1KB. Need to do proper measurements.
ImU32 ImHash(const void* data, int data_size, ImU32 seed) ImU32 ImHash(const void* data, int data_size, ImU32 seed)
{ {
static ImU32 crc32_lut[256] = { 0 };
if (!crc32_lut[1])
{
const ImU32 polynomial = 0xEDB88320;
for (ImU32 i = 0; i < 256; i++)
{
ImU32 crc = i;
for (ImU32 j = 0; j < 8; j++)
crc = (crc >> 1) ^ (ImU32(-int(crc & 1)) & polynomial);
crc32_lut[i] = crc;
}
}
seed = ~seed; seed = ~seed;
ImU32 crc = seed; ImU32 crc = seed;
const unsigned char* current = (const unsigned char*)data; const unsigned char* current = (const unsigned char*)data;
const ImU32* crc32_lut = GCrc32LookupTable;
if (data_size > 0) if (data_size > 0)
{ {
@ -2536,6 +2547,7 @@ ImGuiWindow::~ImGuiWindow()
ImGuiID ImGuiWindow::GetID(const char* str, const char* str_end) ImGuiID ImGuiWindow::GetID(const char* str, const char* str_end)
{ {
// FIXME: ImHash with str_end doesn't behave same as with identical zero-terminated string, because of ### handling.
ImGuiID seed = IDStack.back(); ImGuiID seed = IDStack.back();
ImGuiID id = ImHash(str, str_end ? (int)(str_end - str) : 0, seed); ImGuiID id = ImHash(str, str_end ? (int)(str_end - str) : 0, seed);
ImGui::KeepAliveID(id); ImGui::KeepAliveID(id);