unsigned int zcrc32(const void *data, int size, unsigned int init_value) {
  char *p = (char *)data;
  int len = size;
  register unsigned int crc;
  static unsigned int crc32tab[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,
  };
  crc = init_value ^ 0xFFFFFFFF;
  for (; len--; p++) {
    crc = ((crc >> 8) & 0x00FFFFFF) ^ crc32tab[(crc ^ (*p)) & 0xFF];
  }
  return (crc ^ 0xFFFFFFFF);
}


x86 assembly (clang, -O0):
<zcrc32>:
push   %rbp
mov    %rsp,%rbp
mov    %rdi,-0x8(%rbp)
mov    %esi,-0xc(%rbp)
mov    %edx,-0x10(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,-0x18(%rbp)
mov    -0xc(%rbp),%eax
mov    %eax,-0x1c(%rbp)
mov    -0x10(%rbp),%eax
xor    $0xffffffff,%eax
mov    %eax,-0x20(%rbp)
mov    -0x1c(%rbp),%eax
mov    %eax,%ecx
add    $0xffffffff,%ecx
mov    %ecx,-0x1c(%rbp)
cmp    $0x0,%eax
je     1178 <zcrc32+0x78>
mov    -0x20(%rbp),%eax
shr    $0x8,%eax
and    $0xffffff,%eax
mov    -0x20(%rbp),%ecx
mov    -0x18(%rbp),%rdx
movsbl (%rdx),%edx
xor    %edx,%ecx
and    $0xff,%ecx
mov    %ecx,%ecx
mov    %ecx,%edx
lea    0x2ecf(%rip),%rcx
xor    (%rcx,%rdx,4),%eax
mov    %eax,-0x20(%rbp)
mov    -0x18(%rbp),%rax
add    $0x1,%rax
mov    %rax,-0x18(%rbp)
jmp    1125 <zcrc32+0x25>
mov    -0x20(%rbp),%eax
xor    $0xffffffff,%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<zcrc32>:
not    %edx
test   %esi,%esi
je     1116 <zcrc32+0x16>
test   $0x1,%sil
jne    111b <zcrc32+0x1b>
mov    %esi,%r8d
cmp    $0x1,%esi
jne    1141 <zcrc32+0x41>
jmp    117a <zcrc32+0x7a>
mov    %edx,%eax
not    %eax
ret
lea    -0x1(%rsi),%r8d
mov    %edx,%eax
shr    $0x8,%eax
movzbl (%rdi),%ecx
movzbl %dl,%edx
xor    %ecx,%edx
lea    0xecd(%rip),%rcx
xor    (%rcx,%rdx,4),%eax
add    $0x1,%rdi
mov    %eax,%edx
cmp    $0x1,%esi
je     117a <zcrc32+0x7a>
mov    %r8d,%r8d
xor    %esi,%esi
lea    0xeb3(%rip),%r9
mov    %edx,%eax
nop
movzbl %al,%edx
shr    $0x8,%eax
movzbl (%rdi,%rsi,1),%ecx
xor    %ecx,%edx
xor    (%r9,%rdx,4),%eax
movzbl %al,%ecx
shr    $0x8,%eax
movzbl 0x1(%rdi,%rsi,1),%edx
xor    %edx,%ecx
xor    (%r9,%rcx,4),%eax
add    $0x2,%rsi
cmp    %esi,%r8d
jne    1150 <zcrc32+0x50>
not    %eax
ret

LLVM IR (-O0):
@zcrc32.crc32tab = internal global [256 x i32] [i32 0, i32 1996959894, i32 -301047508, i32 -1727442502, i32 124634137, i32 1886057615, i32 -379345611, i32 -1637575261, i32 249268274, i32 2044508324, i32 -522852066, i32 -1747789432, i32 162941995, i32 2125561021, i32 -407360249, i32 -1866523247, i32 498536548, i32 1789927666, i32 -205950648, i32 -2067906082, i32 450548861, i32 1843258603, i32 -187386543, i32 -2083289657, i32 325883990, i32 1684777152, i32 -43845254, i32 -1973040660, i32 335633487, i32 1661365465, i32 -99664541, i32 -1928851979, i32 997073096, i32 1281953886, i32 -715111964, i32 -1570279054, i32 1006888145, i32 1258607687, i32 -770865667, i32 -1526024853, i32 901097722, i32 1119000684, i32 -608450090, i32 -1396901568, i32 853044451, i32 1172266101, i32 -589951537, i32 -1412350631, i32 651767980, i32 1373503546, i32 -925412992, i32 -1076862698, i32 565507253, i32 1454621731, i32 -809855591, i32 -1195530993, i32 671266974, i32 1594198024, i32 -972236366, i32 -1324619484, i32 795835527, i32 1483230225, i32 -1050600021, i32 -1234817731, i32 1994146192, i32 31158534, i32 -1731059524, i32 -271249366, i32 1907459465, i32 112637215, i32 -1614814043, i32 -390540237, i32 2013776290, i32 251722036, i32 -1777751922, i32 -519137256, i32 2137656763, i32 141376813, i32 -1855689577, i32 -429695999, i32 1802195444, i32 476864866, i32 -2056965928, i32 -228458418, i32 1812370925, i32 453092731, i32 -2113342271, i32 -183516073, i32 1706088902, i32 314042704, i32 -1950435094, i32 -54949764, i32 1658658271, i32 366619977, i32 -1932296973, i32 -69972891, i32 1303535960, i32 984961486, i32 -1547960204, i32 -725929758, i32 1256170817, i32 1037604311, i32 -1529756563, i32 -740887301, i32 1131014506, i32 879679996, i32 -1385723834, i32 -631195440, i32 1141124467, i32 855842277, i32 -1442165665, i32 -586318647, i32 1342533948, i32 654459306, i32 -1106571248, i32 -921952122, i32 1466479909, i32 544179635, i32 -1184443383, i32 -832445281, i32 1591671054, i32 702138776, i32 -1328506846, i32 -942167884, i32 1504918807, i32 783551873, i32 -1212326853, i32 -1061524307, i32 -306674912, i32 -1698712650, i32 62317068, i32 1957810842, i32 -355121351, i32 -1647151185, i32 81470997, i32 1943803523, i32 -480048366, i32 -1805370492, i32 225274430, i32 2053790376, i32 -468791541, i32 -1828061283, i32 167816743, i32 2097651377, i32 -267414716, i32 -2029476910, i32 503444072, i32 1762050814, i32 -144550051, i32 -2140837941, i32 426522225, i32 1852507879, i32 -19653770, i32 -1982649376, i32 282753626, i32 1742555852, i32 -105259153, i32 -1900089351, i32 397917763, i32 1622183637, i32 -690576408, i32 -1580100738, i32 953729732, i32 1340076626, i32 -776247311, i32 -1497606297, i32 1068828381, i32 1219638859, i32 -670225446, i32 -1358292148, i32 906185462, i32 1090812512, i32 -547295293, i32 -1469587627, i32 829329135, i32 1181335161, i32 -882789492, i32 -1134132454, i32 628085408, i32 1382605366, i32 -871598187, i32 -1156888829, i32 570562233, i32 1426400815, i32 -977650754, i32 -1296233688, i32 733239954, i32 1555261956, i32 -1026031705, i32 -1244606671, i32 752459403, i32 1541320221, i32 -1687895376, i32 -328994266, i32 1969922972, i32 40735498, i32 -1677130071, i32 -351390145, i32 1913087877, i32 83908371, i32 -1782625662, i32 -491226604, i32 2075208622, i32 213261112, i32 -1831694693, i32 -438977011, i32 2094854071, i32 198958881, i32 -2032938284, i32 -237706686, i32 1759359992, i32 534414190, i32 -2118248755, i32 -155638181, i32 1873836001, i32 414664567, i32 -2012718362, i32 -15766928, i32 1711684554, i32 285281116, i32 -1889165569, i32 -127750551, i32 1634467795, i32 376229701, i32 -1609899400, i32 -686959890, i32 1308918612, i32 956543938, i32 -1486412191, i32 -799009033, i32 1231636301, i32 1047427035, i32 -1362007478, i32 -640263460, i32 1088359270, i32 936918000, i32 -1447252397, i32 -558129467, i32 1202900863, i32 817233897, i32 -1111625188, i32 -893730166, i32 1404277552, i32 615818150, i32 -1160759803, i32 -841546093, i32 1423857449, i32 601450431, i32 -1285129682, i32 -1000256840, i32 1567103746, i32 711928724, i32 -1274298825, i32 -1022587231, i32 1510334235, i32 755167117]
define i32 @zcrc32(i8* %0, i32 %1, i32 %2) {
%4 = alloca i8*
%5 = alloca i32
%6 = alloca i32
%7 = alloca i8*
%8 = alloca i32
%9 = alloca i32
store i8* %0, i8** %4
store i32 %1, i32* %5
store i32 %2, i32* %6
%10 = load i8*, i8** %4
store i8* %10, i8** %7
%11 = load i32, i32* %5
store i32 %11, i32* %8
%12 = load i32, i32* %6
%13 = xor i32 %12, -1
store i32 %13, i32* %9
br label %14
14: ; preds = %32, %3
%15 = load i32, i32* %8
%16 = add nsw i32 %15, -1
store i32 %16, i32* %8
%17 = icmp ne i32 %15, 0
br i1 %17, label %18, label %35
18: ; preds = %14
%19 = load i32, i32* %9
%20 = lshr i32 %19, 8
%21 = and i32 %20, 16777215
%22 = load i32, i32* %9
%23 = load i8*, i8** %7
%24 = load i8, i8* %23
%25 = sext i8 %24 to i32
%26 = xor i32 %22, %25
%27 = and i32 %26, 255
%28 = zext i32 %27 to i64
%29 = getelementptr inbounds [256 x i32], [256 x i32]* @zcrc32.crc32tab, i64 0, i64 %28
%30 = load i32, i32* %29
%31 = xor i32 %21, %30
store i32 %31, i32* %9
br label %32
32: ; preds = %18
%33 = load i8*, i8** %7
%34 = getelementptr inbounds i8, i8* %33, i32 1
store i8* %34, i8** %7
br label %14
35: ; preds = %14
%36 = load i32, i32* %9
%37 = xor i32 %36, -1
ret i32 %37
}

LLVM IR (-O2):
@zcrc32.crc32tab = internal unnamed_addr constant [256 x i32] [i32 0, i32 1996959894, i32 -301047508, i32 -1727442502, i32 124634137, i32 1886057615, i32 -379345611, i32 -1637575261, i32 249268274, i32 2044508324, i32 -522852066, i32 -1747789432, i32 162941995, i32 2125561021, i32 -407360249, i32 -1866523247, i32 498536548, i32 1789927666, i32 -205950648, i32 -2067906082, i32 450548861, i32 1843258603, i32 -187386543, i32 -2083289657, i32 325883990, i32 1684777152, i32 -43845254, i32 -1973040660, i32 335633487, i32 1661365465, i32 -99664541, i32 -1928851979, i32 997073096, i32 1281953886, i32 -715111964, i32 -1570279054, i32 1006888145, i32 1258607687, i32 -770865667, i32 -1526024853, i32 901097722, i32 1119000684, i32 -608450090, i32 -1396901568, i32 853044451, i32 1172266101, i32 -589951537, i32 -1412350631, i32 651767980, i32 1373503546, i32 -925412992, i32 -1076862698, i32 565507253, i32 1454621731, i32 -809855591, i32 -1195530993, i32 671266974, i32 1594198024, i32 -972236366, i32 -1324619484, i32 795835527, i32 1483230225, i32 -1050600021, i32 -1234817731, i32 1994146192, i32 31158534, i32 -1731059524, i32 -271249366, i32 1907459465, i32 112637215, i32 -1614814043, i32 -390540237, i32 2013776290, i32 251722036, i32 -1777751922, i32 -519137256, i32 2137656763, i32 141376813, i32 -1855689577, i32 -429695999, i32 1802195444, i32 476864866, i32 -2056965928, i32 -228458418, i32 1812370925, i32 453092731, i32 -2113342271, i32 -183516073, i32 1706088902, i32 314042704, i32 -1950435094, i32 -54949764, i32 1658658271, i32 366619977, i32 -1932296973, i32 -69972891, i32 1303535960, i32 984961486, i32 -1547960204, i32 -725929758, i32 1256170817, i32 1037604311, i32 -1529756563, i32 -740887301, i32 1131014506, i32 879679996, i32 -1385723834, i32 -631195440, i32 1141124467, i32 855842277, i32 -1442165665, i32 -586318647, i32 1342533948, i32 654459306, i32 -1106571248, i32 -921952122, i32 1466479909, i32 544179635, i32 -1184443383, i32 -832445281, i32 1591671054, i32 702138776, i32 -1328506846, i32 -942167884, i32 1504918807, i32 783551873, i32 -1212326853, i32 -1061524307, i32 -306674912, i32 -1698712650, i32 62317068, i32 1957810842, i32 -355121351, i32 -1647151185, i32 81470997, i32 1943803523, i32 -480048366, i32 -1805370492, i32 225274430, i32 2053790376, i32 -468791541, i32 -1828061283, i32 167816743, i32 2097651377, i32 -267414716, i32 -2029476910, i32 503444072, i32 1762050814, i32 -144550051, i32 -2140837941, i32 426522225, i32 1852507879, i32 -19653770, i32 -1982649376, i32 282753626, i32 1742555852, i32 -105259153, i32 -1900089351, i32 397917763, i32 1622183637, i32 -690576408, i32 -1580100738, i32 953729732, i32 1340076626, i32 -776247311, i32 -1497606297, i32 1068828381, i32 1219638859, i32 -670225446, i32 -1358292148, i32 906185462, i32 1090812512, i32 -547295293, i32 -1469587627, i32 829329135, i32 1181335161, i32 -882789492, i32 -1134132454, i32 628085408, i32 1382605366, i32 -871598187, i32 -1156888829, i32 570562233, i32 1426400815, i32 -977650754, i32 -1296233688, i32 733239954, i32 1555261956, i32 -1026031705, i32 -1244606671, i32 752459403, i32 1541320221, i32 -1687895376, i32 -328994266, i32 1969922972, i32 40735498, i32 -1677130071, i32 -351390145, i32 1913087877, i32 83908371, i32 -1782625662, i32 -491226604, i32 2075208622, i32 213261112, i32 -1831694693, i32 -438977011, i32 2094854071, i32 198958881, i32 -2032938284, i32 -237706686, i32 1759359992, i32 534414190, i32 -2118248755, i32 -155638181, i32 1873836001, i32 414664567, i32 -2012718362, i32 -15766928, i32 1711684554, i32 285281116, i32 -1889165569, i32 -127750551, i32 1634467795, i32 376229701, i32 -1609899400, i32 -686959890, i32 1308918612, i32 956543938, i32 -1486412191, i32 -799009033, i32 1231636301, i32 1047427035, i32 -1362007478, i32 -640263460, i32 1088359270, i32 936918000, i32 -1447252397, i32 -558129467, i32 1202900863, i32 817233897, i32 -1111625188, i32 -893730166, i32 1404277552, i32 615818150, i32 -1160759803, i32 -841546093, i32 1423857449, i32 601450431, i32 -1285129682, i32 -1000256840, i32 1567103746, i32 711928724, i32 -1274298825, i32 -1022587231, i32 1510334235, i32 755167117]
define i32 @zcrc32(i8* nocapture %0, i32 %1, i32 %2) {
%4 = xor i32 %2, -1
%5 = icmp eq i32 %1, 0
br i1 %5, label %53, label %6
6: ; preds = %3
%7 = and i32 %1, 1
%8 = icmp eq i32 %7, 0
br i1 %8, label %21, label %9
9: ; preds = %6
%10 = add nsw i32 %1, -1
%11 = lshr i32 %4, 8
%12 = load i8, i8* %0
%13 = zext i8 %12 to i32
%14 = and i32 %4, 255
%15 = xor i32 %14, %13
%16 = zext i32 %15 to i64
%17 = getelementptr inbounds [256 x i32], [256 x i32]* @zcrc32.crc32tab, i64 0, i64 %16
%18 = load i32, i32* %17
%19 = xor i32 %18, %11
%20 = getelementptr inbounds i8, i8* %0, i64 1
br label %21
21: ; preds = %9, %6
%22 = phi i32 [ undef, %6 ], [ %19, %9 ]
%23 = phi i32 [ %4, %6 ], [ %19, %9 ]
%24 = phi i32 [ %1, %6 ], [ %10, %9 ]
%25 = phi i8* [ %0, %6 ], [ %20, %9 ]
%26 = icmp eq i32 %1, 1
br i1 %26, label %53, label %27
27: ; preds = %21, %27
%28 = phi i32 [ %50, %27 ], [ %23, %21 ]
%29 = phi i32 [ %41, %27 ], [ %24, %21 ]
%30 = phi i8* [ %51, %27 ], [ %25, %21 ]
%31 = lshr i32 %28, 8
%32 = load i8, i8* %30
%33 = zext i8 %32 to i32
%34 = and i32 %28, 255
%35 = xor i32 %34, %33
%36 = zext i32 %35 to i64
%37 = getelementptr inbounds [256 x i32], [256 x i32]* @zcrc32.crc32tab, i64 0, i64 %36
%38 = load i32, i32* %37
%39 = xor i32 %38, %31
%40 = getelementptr inbounds i8, i8* %30, i64 1
%41 = add nsw i32 %29, -2
%42 = lshr i32 %39, 8
%43 = load i8, i8* %40
%44 = zext i8 %43 to i32
%45 = and i32 %39, 255
%46 = xor i32 %45, %44
%47 = zext i32 %46 to i64
%48 = getelementptr inbounds [256 x i32], [256 x i32]* @zcrc32.crc32tab, i64 0, i64 %47
%49 = load i32, i32* %48
%50 = xor i32 %49, %42
%51 = getelementptr inbounds i8, i8* %30, i64 2
%52 = icmp eq i32 %41, 0
br i1 %52, label %53, label %27
53: ; preds = %21, %27, %3
%54 = phi i32 [ %4, %3 ], [ %22, %21 ], [ %50, %27 ]
%55 = xor i32 %54, -1
ret i32 %55
}