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libbb: faster and smaller decode_base32()

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function                                             old     new   delta
decode_base32                                        275     224     -51

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2020-11-27 21:25:34 +01:00
parent 170b8628fa
commit 2cd37d65e2
1 changed files with 34 additions and 50 deletions
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84
libbb/uuencode.c
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@ -82,7 +82,7 @@ void FAST_FUNC bb_uuencode(char *p, const void *src, int length, const char *tbl
}
/*
* Decode base64 encoded string. Stops on NUL after terminating "=" or "==".
* Decode base64 encoded string.
*
* Returns: pointer to the undecoded part of source.
* If points to '\0', then the source was fully decoded.
@ -139,61 +139,45 @@ const char* FAST_FUNC decode_base64(char **pp_dst, const char *src)
const char* FAST_FUNC decode_base32(char **pp_dst, const char *src)
{
char *dst = *pp_dst;
const char *src_tail;
uint64_t ch = 0;
int i = 0;
while (1) {
unsigned char five_bit[8];
int count = 0;
while (*src) {
int t = (unsigned char)*src++;
/* Fetch up to eight 5-bit values */
src_tail = src;
while (count < 8) {
char *table_ptr;
int ch;
/* "if" forest is faster than strchr(bb_uuenc_tbl_base32, t) */
if (t >= '2' && t <= '7')
t = t - '2' + 26;
else if ((t|0x20) >= 'a' && (t|0x20) <= 'z')
t = (t|0x20) - 'a';
else if (t == '=' && i > 1)
t = 0;
else
//TODO: add BASE64_FLAG_foo to die on bad char?
continue;
/* Get next _valid_ character.
* bb_uuenc_tbl_base32[] contains this string:
* 0 1 2 3
* 01234567890123456789012345678901
* "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567="
*/
do {
ch = *src;
if (ch == '\0') {
if (count == 0) {
src_tail = src;
}
goto ret;
}
src++;
table_ptr = strchr(bb_uuenc_tbl_base32, toupper(ch));
} while (!table_ptr);
/* Convert encoded character to decimal */
ch = table_ptr - bb_uuenc_tbl_base32;
/* ch is 32 if char was '=', otherwise 0..31 */
if (ch == 32)
ch = (ch << 5) | t;
if (++i == 8) {
*dst++ = (char) (ch >> 32);
*dst++ = (char) (ch >> 24);
*dst++ = (char) (ch >> 16);
*dst++ = (char) (ch >> 8);
*dst++ = (char) ch;
if (t == 0 && src[-1] == '=') { /* was last input char '='? */
const char *s = src;
while (*--s == '=' && --i != 0)
continue;
i = 8 - i; /* count of =, must be 1, 3, 4 or 6 */
dst -= (i+1) * 2 / 3; /* discard last 1, 2, 3 or 4 bytes */
i = 0;
break;
five_bit[count] = ch;
count++;
}
i = 0;
}
/* Transform 5-bit values to 8-bit ones */
if (count > 1) // xxxxx xxx-- ----- ----- ----- ----- ----- -----
*dst++ = five_bit[0] << 3 | five_bit[1] >> 2;
if (count > 3) // ----- ---xx xxxxx x---- ----- ----- ----- -----
*dst++ = five_bit[1] << 6 | five_bit[2] << 1 | five_bit[3] >> 4;
if (count > 4) // ----- ----- ----- -xxxx xxxx- ----- ----- -----
*dst++ = five_bit[3] << 4 | five_bit[4] >> 1;
if (count > 6) // ----- ----- ----- ----- ----x xxxxx xx--- -----
*dst++ = five_bit[4] << 7 | five_bit[5] << 2 | five_bit[6] >> 3;
if (count > 7) // ----- ----- ----- ----- ----- ----- --xxx xxxxx
*dst++ = five_bit[6] << 5 | five_bit[7];
} /* while (1) */
ret:
}
*pp_dst = dst;
return src_tail;
/* i should be zero here if full 8-char block was decoded */
return src - i;
}
#endif