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libbb: smaller and faster decode_base64()

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function                                             old     new   delta
decode_base64                                        195     180     -15

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2020-11-27 20:44:55 +01:00
parent dc68a5ddac
commit 170b8628fa
2 changed files with 36 additions and 101 deletions
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100
libbb/uuencode.c
View File

@ -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 '\0'.
* Decode base64 encoded string. Stops on NUL after terminating "=" or "==".
*
* Returns: pointer to the undecoded part of source.
* If points to '\0', then the source was fully decoded.
@ -91,76 +91,48 @@ void FAST_FUNC bb_uuencode(char *p, const void *src, int length, const char *tbl
const char* FAST_FUNC decode_base64(char **pp_dst, const char *src)
{
char *dst = *pp_dst;
const char *src_tail;
unsigned ch = 0;
int i = 0;
while (1) {
unsigned char six_bit[4];
int count = 0;
while (*src) {
int t = (unsigned char)*src++;
/* Fetch up to four 6-bit values */
src_tail = src;
while (count < 4) {
char *table_ptr;
int ch;
/* Get next _valid_ character.
* bb_uuenc_tbl_base64[] contains this string:
* 0 1 2 3 4 5 6
* 01234567890123456789012345678901234567890123456789012345678901234
* "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
*/
do {
ch = *src;
if (ch == '\0') {
if (count == 0) {
/* Example:
* If we decode "QUJD <NUL>", we want
* to return ptr to NUL, not to ' ',
* because we did fully decode
* the string (to "ABC").
*/
src_tail = src;
}
goto ret;
}
src++;
table_ptr = strchr(bb_uuenc_tbl_base64, ch);
/* "if" forest is faster than strchr(bb_uuenc_tbl_base64, t) */
if (t >= '0' && t <= '9')
t = t - '0' + 52;
else if (t >= 'A' && t <= 'Z')
t = t - 'A';
else if (t >= 'a' && t <= 'z')
t = t - 'a' + 26;
else if (t == '+')
t = 62;
else if (t == '/')
t = 63;
else if (t == '=' && (i == 3 || (i == 2 && *src == '=')))
/* the above disallows "==AA", "A===", "AA=A" etc */
t = 0x1000000;
else
//TODO: add BASE64_FLAG_foo to die on bad char?
} while (!table_ptr);
continue;
/* Convert encoded character to decimal */
ch = table_ptr - bb_uuenc_tbl_base64;
/* ch is 64 if char was '=', otherwise 0..63 */
if (ch == 64)
ch = (ch << 6) | t;
if (++i == 4) {
*dst++ = (char) (ch >> 16);
*dst++ = (char) (ch >> 8);
*dst++ = (char) ch;
i = 0;
if (ch & 0x1000000) { /* was last input char '='? */
dst--;
if (ch & (0x1000000 << 6)) /* was it "=="? */
dst--;
break;
six_bit[count] = ch;
count++;
}
/* Transform 6-bit values to 8-bit ones.
* count can be < 4 when we decode the tail:
* "eQ==" -> "y", not "y NUL NUL".
* Note that (count > 1) is always true,
* "x===" encoding is not valid:
* even a single zero byte encodes as "AA==".
* However, with current logic we come here with count == 1
* when we decode "==" tail.
*/
if (count > 1)
*dst++ = six_bit[0] << 2 | six_bit[1] >> 4;
if (count > 2)
*dst++ = six_bit[1] << 4 | six_bit[2] >> 2;
if (count > 3)
*dst++ = six_bit[2] << 6 | six_bit[3];
/* Note that if we decode "AA==" and ate first '=',
* we just decoded one char (count == 2) and now we'll
* do the loop once more to decode second '='.
*/
} /* while (1) */
ret:
ch = 0;
}
}
*pp_dst = dst;
return src_tail;
/* i should be zero here if full 4-char block was decoded */
return src - i; /* -i rejects truncations: e.g. "MQ" and "MQ=" (correct encoding is "MQ==" -> "1") */
}
#if ENABLE_BASE32

37
networking/httpd.c
View File

@ -1017,46 +1017,9 @@ static char *encodeString(const char *string)
*/
static void decodeBase64(char *Data)
{
# if ENABLE_BASE64 || ENABLE_UUDECODE
/* Call decode_base64() from uuencode.c */
char *eptr = Data;
decode_base64(&eptr, Data);
*eptr = '\0';
# else
const unsigned char *in = (const unsigned char *)Data;
/* The decoded size will be at most 3/4 the size of the encoded */
unsigned ch = 0;
int i = 0;
while (*in) {
int t = *in++;
if (t >= '0' && t <= '9')
t = t - '0' + 52;
else if (t >= 'A' && t <= 'Z')
t = t - 'A';
else if (t >= 'a' && t <= 'z')
t = t - 'a' + 26;
else if (t == '+')
t = 62;
else if (t == '/')
t = 63;
else if (t == '=')
t = 0;
else
continue;
ch = (ch << 6) | t;
i++;
if (i == 4) {
*Data++ = (char) (ch >> 16);
*Data++ = (char) (ch >> 8);
*Data++ = (char) ch;
i = 0;
}
}
*Data = '\0';
# endif
}
#endif