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package gitdiff
import (
"fmt"
)
var (
b85Table map[byte]byte
b85Alpha = []byte(
"0123456789" + "ABCDEFGHIJKLMNOPQRSTUVWXYZ" + "abcdefghijklmnopqrstuvwxyz" + "!#$%&()*+-;<=>?@^_`{|}~",
)
)
func init() {
b85Table = make(map[byte]byte)
for i, c := range b85Alpha {
b85Table[c] = byte(i)
}
}
// base85Decode decodes Base85-encoded data from src into dst. It uses the
// alphabet defined by base85.c in the Git source tree. src must contain at
// least len(dst) bytes of encoded data.
func base85Decode(dst, src []byte) error {
var v uint32
var n, ndst int
for i, b := range src {
if b, ok := b85Table[b]; ok {
v = 85*v + uint32(b)
n++
} else {
return fmt.Errorf("invalid base85 byte at index %d: 0x%X", i, src[i])
}
if n == 5 {
rem := len(dst) - ndst
for j := 0; j < 4 && j < rem; j++ {
dst[ndst] = byte(v >> 24)
ndst++
v <<= 8
}
v = 0
n = 0
}
}
if n > 0 {
return fmt.Errorf("base85 data terminated by underpadded sequence")
}
if ndst < len(dst) {
return fmt.Errorf("base85 data underrun: %d < %d", ndst, len(dst))
}
return nil
}
// base85Encode encodes src in Base85, writing the result to dst. It uses the
// alphabet defined by base85.c in the Git source tree.
func base85Encode(dst, src []byte) {
var di, si int
encode := func(v uint32) {
dst[di+0] = b85Alpha[(v/(85*85*85*85))%85]
dst[di+1] = b85Alpha[(v/(85*85*85))%85]
dst[di+2] = b85Alpha[(v/(85*85))%85]
dst[di+3] = b85Alpha[(v/85)%85]
dst[di+4] = b85Alpha[v%85]
}
n := (len(src) / 4) * 4
for si < n {
encode(uint32(src[si+0])<<24 | uint32(src[si+1])<<16 | uint32(src[si+2])<<8 | uint32(src[si+3]))
si += 4
di += 5
}
var v uint32
switch len(src) - si {
case 3:
v |= uint32(src[si+2]) << 8
fallthrough
case 2:
v |= uint32(src[si+1]) << 16
fallthrough
case 1:
v |= uint32(src[si+0]) << 24
encode(v)
}
}
// base85Len returns the length of n bytes of Base85 encoded data.
func base85Len(n int) int {
return (n + 3) / 4 * 5
}
|
