Initial arm64 crc32

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+title:ARM64 assembly crc32
+keywords:assembly,m1,arm64,macos,linux
+
+# ARM64 assembly crc32
+
+## Intro
+
+Latest ARM64 processors support hardware crc32 instruction, since architecture version __ARMv8.1-A__ .
+Raspbery pi have architecture version __ARMv8-A__ version and Apple M1 __ARMv8.4-A__. Both of those 
+have hardware accelerated crc32 instruction. In example is shown how to use software and hardware implementation of
+that functionality for macos and linux.
+
+## Verify architecture
+
+### Raspberry Pi 4
+
+Run command
+```
+uname -a
+Linux raspberrypi 5.4.42-v8+ #1319 SMP PREEMPT Wed May 20 14:18:56 BST 2020 aarch64 GNU/Linux
+```
+There is substring "aarch64" that indicates that os bitnes is 64bit 
+
+To check if CPU supports crc32 instructions run
+```
+cat /proc/cpuinfo | grep crc
+```
+check for "crc32" substring
+
+### Apple M1
+
+If you have Apple M1 then you already know it. If not sure run one of those commands to verify archirecture
+
+```
+uname -a 
+```
+
+or 
+```
+arch
+```
+
+in output string should be "arm64" 
+
+## ARM64 crc32 instructions
+
+Wiki have table with all different kind of implementation of crc32 https://en.wikipedia.org/wiki/Cyclic_redundancy_check 
+arm64 crc32 implementation reffered in wiki table as __CRC-32__. There is support also for __CRC-32C__.
+
+There is 4 types of crc32 instruction for 1,2,4,8 byte of data that are marked with
+postfix b,h,w,x.
+Wraped up examples of instructions:
+```c
+#define CRC32X(crc, value) __asm__("crc32x %w[c], %w[c], %x[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32W(crc, value) __asm__("crc32w %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32H(crc, value) __asm__("crc32h %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32B(crc, value) __asm__("crc32b %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32CX(crc, value) __asm__("crc32cx %w[c], %w[c], %x[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32CW(crc, value) __asm__("crc32cw %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32CH(crc, value) __asm__("crc32ch %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32CB(crc, value) __asm__("crc32cb %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
+```
+
+https://android.googlesource.com/platform/external/linux-kselftest/+/d97034ccdf0a13ad86f00945df245bbaf0780478/arch/arm64/crypto/crc32-arm64.c
+
+## Software implementation
+
+Found crc32 software implementation as its helps verify HW instruction results. It verify that
+algorithm used is correct against CRC32 table in wiki and that there is no other quirks for using crc32.
+
+Short implementation of crc32 with initial table generation
+
+http://home.thep.lu.se/~bjorn/crc/
+
+There is implementation from BSD kernel where crc32 value tables are precalculated.
+
+https://web.mit.edu/freebsd/head/sys/libkern/crc32.c
+
+```c
+uint32_t crc32_for_byte(uint32_t r) {
+  for(int j = 0; j < 8; ++j)
+    r = (r & 1? 0: (uint32_t)0xEDB88320L) ^ r >> 1;
+  return r ^ (uint32_t)0xFF000000L;
+}
+
+void crc32(const void *data, size_t n_bytes, uint32_t* crc) {
+  static uint32_t table[0x100];
+  if(!*table)
+    for(size_t i = 0; i < 0x100; ++i)
+      table[i] = crc32_for_byte(i);
+  for(size_t i = 0; i < n_bytes; ++i)
+    *crc = table[(uint8_t)*crc ^ ((uint8_t*)data)[i]] ^ *crc >> 8;
+}
+```
+
+## HW and SW implementation differences
+
+when using assembly instruction please note that initial value of crc is __crc=0xffffffff__
+and final result should be inverted __~crc__ to match software implementation where
+initial values is __crc=0x0__ and final result not need to be preprocessed.
+
+
+## Source code
+```c
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <stdint.h>
+
+/*
+https://android.googlesource.com/platform/external/linux-kselftest/+/d97034ccdf0a13ad86f00945df245bbaf0780478/arch/arm64/crypto/crc32-arm64.c
+*/
+#define CRC32X(crc, value) __asm__("crc32x %w[c], %w[c], %x[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32W(crc, value) __asm__("crc32w %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32H(crc, value) __asm__("crc32h %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32B(crc, value) __asm__("crc32b %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32CX(crc, value) __asm__("crc32cx %w[c], %w[c], %x[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32CW(crc, value) __asm__("crc32cw %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32CH(crc, value) __asm__("crc32ch %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
+#define CRC32CB(crc, value) __asm__("crc32cb %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
+
+/*
+http://home.thep.lu.se/~bjorn/crc/
+*/
+
+uint32_t crc32_for_byte(uint32_t r) {
+  for(int j = 0; j < 8; ++j)
+    r = (r & 1? 0: (uint32_t)0xEDB88320L) ^ r >> 1;
+  return r ^ (uint32_t)0xFF000000L;
+}
+
+static uint32_t crc32_tab_ver1[0x100];
+void crc32_ver1(const void *data, size_t n_bytes, uint32_t* crc) {
+  static uint32_t table[0x100];
+  if(!*table)
+    for(size_t i = 0; i < 0x100; ++i)
+      crc32_tab_ver1[i] = crc32_for_byte(i);
+  for(size_t i = 0; i < n_bytes; ++i)
+    *crc = crc32_tab_ver1[(uint8_t)*crc ^ ((uint8_t*)data)[i]] ^ *crc >> 8;
+}
+
+/*
+https://web.mit.edu/freebsd/head/sys/libkern/crc32.c
+*/
+const uint32_t crc32_tab_ver2[] = {
+	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
+};
+
+uint32_t crc32_ver2(const void *buf, size_t size)
+{
+	const uint8_t *p = buf;
+	uint32_t crc;
+
+	crc = ~0U;
+	while (size--)
+		crc = crc32_tab_ver2[(crc ^ *p++) & 0xFF] ^ (crc >> 8);
+	return crc ^ ~0U;
+}
+
+static uint8_t test_data[] = {0xaa,0xbb,0xcc,0xdd,0xee,0xff,0x00,0x11};
+
+int main() {
+	size_t i=0;
+
+	uint32_t crc_1=0x00000000, crc_2=0x00000000, crc_3=0xffffffff;
+
+	printf("Initial values:      SW1:%08x SW2:%08x HW:%08x\n",crc_1,crc_2,crc_3);
+	for (i=0;i<sizeof(test_data);i++) {
+		CRC32B(crc_3,test_data[i]);
+	}
+	crc32_ver1(test_data, sizeof(test_data),&crc_1);
+	crc_2 = crc32_ver2(test_data,sizeof(test_data));
+	printf("Final result:        SW1:%08x SW2:%08x HW:%08x\n",crc_1,crc_2,~crc_3);
+}
+```
+## Compile
+
+### Raspbery Pi 4
+
+```
+gcc asm_crc32.c -o asm_crc32 -march=armv8.1-a
+```
+
+### Apple M1
+
+```
+gcc asm_crc32.c -o asm_crc32
+```
+
+## Links
+
+[01]https://en.wikipedia.org/wiki/Cyclic_redundancy_check  
+[02]http://home.thep.lu.se/~bjorn/crc/  
+[03]https://web.mit.edu/freebsd/head/sys/libkern/crc32.c  
+[04]https://developer.arm.com/documentation/dui0801/g/A32-and-T32-Instructions/CRC32  
+[05]https://en.wikipedia.org/wiki/Mathematics_of_cyclic_redundancy_checks#Polynomial_representations  
+[06]https://stackoverflow.com/questions/60693089/what-initial-value-should-i-pass-to-the-aarch64-crc32-instructions  
+[07]https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html  
+[08][main.lv/writeup/arm64_assembly_hello_world.md](/writeup/arm64_assembly_hello_world.md)