diff options
Diffstat (limited to 'md/writeup')
| -rw-r--r-- | md/writeup/arm64_assembly_crc32.md | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/md/writeup/arm64_assembly_crc32.md b/md/writeup/arm64_assembly_crc32.md index c284349..48ffd21 100644 --- a/md/writeup/arm64_assembly_crc32.md +++ b/md/writeup/arm64_assembly_crc32.md @@ -12,6 +12,9 @@ that functionality for macos and linux. ## Verify architecture +Before running any of this code, check that archirecture is correct in case of Apple M1 its easiest to do. +With Raspberry Pi 4 need to run it with 64bit linux. + ### Raspberry Pi 4 Run command @@ -19,13 +22,13 @@ 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 +There is substring "aarch64" that indicates that os supports 64 bits To check if CPU supports crc32 instructions run ``` cat /proc/cpuinfo | grep crc ``` -check for "crc32" substring +search for "crc32" substring ### Apple M1 @@ -45,16 +48,18 @@ 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__. +arm64 crc32 implementation reffered in wiki table as __CRC-32__. There is support also for __CRC-32C__ variant. 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 +//crc32 #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)) +//crc32c #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)) @@ -101,6 +106,10 @@ initial values is __crc=0x0__ and final result not need to be preprocessed. ## Source code + +Here is complete source code of software and hardware crc32, that runs over some array of data and compares +results of 2 software implementations and hardware. + ```c #include <stdlib.h> #include <stdio.h> @@ -218,13 +227,13 @@ int main() { ## Compile ### Raspbery Pi 4 - +Need to set extra *-march* option to enable architecture variant that supports crc. ``` gcc asm_crc32.c -o asm_crc32 -march=armv8.1-a ``` ### Apple M1 - +Works without extra options ``` gcc asm_crc32.c -o asm_crc32 ``` |