crc32.go

package main

import (
	"fmt"
	"hash/crc32"
)

var crcTable = crc32.MakeTable(crc32.Castagnoli)

// crc implements the checksum specified in section 3 of
// https://github.com/google/snappy/blob/master/framing_format.txt
func crc(b []byte) uint32 {
	c := crc32.Update(0, crcTable, b)
	return uint32(c>>15|c<<17) + 0xa282ead8
}

// func update(crc uint32, tab *Table, p []byte) uint32 {
// 	crc = ^crc
// 	for _, v := range p {
// 		crc = tab[byte(crc)^v] ^ (crc >> 8)
// 	}
// 	return ^crc
// }

func main() {
	fmt.Println(crc([]byte("123")))
	//31919054
}

emitLiteral.go

package main
import "fmt";
const (
	tagLiteral = 0x00
)


func emitLiteral(dst, lit []byte) int {
	i, n := 0, uint(len(lit)-1)
	switch {
	case n < 60:
		dst[0] = uint8(n)<<2 | tagLiteral
		i = 1
	case n < 1<<8:
		dst[0] = 60<<2 | tagLiteral
		dst[1] = uint8(n)
		i = 2
	case n < 1<<16:
		dst[0] = 61<<2 | tagLiteral
		dst[1] = uint8(n)
		dst[2] = uint8(n >> 8)
		i = 3
	case n < 1<<24:
		dst[0] = 62<<2 | tagLiteral
		dst[1] = uint8(n)
		dst[2] = uint8(n >> 8)
		dst[3] = uint8(n >> 16)
		i = 4
	case int64(n) < 1<<32:
		dst[0] = 63<<2 | tagLiteral
		dst[1] = uint8(n)
		dst[2] = uint8(n >> 8)
		dst[3] = uint8(n >> 16)
		dst[4] = uint8(n >> 24)
		i = 5
	default:
		panic("snappy: source buffer is too long")
	}
	if copy(dst[i:], lit) != len(lit) {
		panic("snappy: destination buffer is too short")
	}
	return i + len(lit)
}
func main() {
    dst:=make([]byte, 12);
    lit:=[]byte("123");
    
    emitLiteral(dst,lit)
    fmt.Println(dst,lit)
}