CRC-32: Difference between revisions

Line 2,110:

It costs less to recompute polynomal shift for each character than indexing

with external tools like <code>awk</code> or <code>tr</code>.

<lang ~~Bash~~>#!/bin/sh

<lang bash>#!/usr/bin/env sh

# POSIX Shell CRC32 of string

# @Name: crc32.sh

# @Version: 1.0.0

# @Version: 1.0.1

# @Author: Léa Gris <lea.gris@noiraude.net>

# @Date: Wed, 27 Mar 2019

Line 2,128:

crc32_stream() {

crc=0xFFFFFFFF # The Initial CRC32 value

p=0xedb88320 # The CRC32 ~~polynomal~~

p=0xedb88320 # The CRC32 polynomial

r=0 # The ~~polynomal~~ reminder

r=0 # The polynomial reminder

c='' # The current character

byte=0 # ~~Tge~~ byte value of the current character

byte=0 # The byte value of the current character

# Iterates each character of the input stream

while c="$(dd bs=1 count=1 2>/dev/null)" && [ -n "$c" ]; do

byte=$(printf '%d' "'${c}") # Converts the character into its byte value

byte=$(printf '%d' "'$c") # Converts the character into its byte value

r=$(((crc & 0xff) ^ byte)) # XOR LSB of CRC with current byte

# 8-bit lsb shift with XOR polynomial reminder when odd

b=0 # bit index

# ~~8-bit~~ ~~lsb~~ ~~shift~~ ~~with~~ ~~XOR~~ ~~polynomal~~ ~~reminder~~ ~~when~~ ~~odd~~

for _ in _ _ _ _ _ _ _ _; do

~~while~~ [ ~~$((b <= 7)) -ne 0 ] && b~~=$((b + 1))~~; do~~

t=$((r >> 1))

r=$(((r & ~~0x1~~) ? ~~(r >> 1)~~ ^ p : ~~r >> 1~~))

r=$(((r & 1) ? t ^ p : t))

done

crc=$(((crc >> 8) ^ r)) # XOR MSB of CRC with Reminder

Line 2,148:

}

# Computes the CRC32 of argument string

# Computes the CRC32 of the argument string

# 1: The argument string

# >&1: The CRC32 integer of the argument string

crc32_string() {

[ $# -eq 1 ] || return # argument required

# Streams with printf to prevent ~~postfixing~~ the string

# Streams with printf to prevent suffixing the string

# with a newline, since echo -n is not available in POSIX Shell

printf '%s' "$1" | crc32_stream