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libbb: shrink base64 decoding a bit

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function                                             old     new   delta
bb_uuenc_tbl_base64                                   67      66      -1
decode_base64                                        182     161     -21

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2011-10-28 16:15:00 +02:00
parent 73d249e704
commit e6094d95b5
1 changed files with 23 additions and 19 deletions
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42
libbb/uuencode.c
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@ -10,7 +10,7 @@
#include "libbb.h" #include "libbb.h"
/* Conversion table. for base 64 */ /* Conversion table. for base 64 */
const char bb_uuenc_tbl_base64[65 + 2] ALIGN1 = { const char bb_uuenc_tbl_base64[65 + 1] ALIGN1 = {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
@ -20,7 +20,7 @@ const char bb_uuenc_tbl_base64[65 + 2] ALIGN1 = {
'w', 'x', 'y', 'z', '0', '1', '2', '3', 'w', 'x', 'y', 'z', '0', '1', '2', '3',
'4', '5', '6', '7', '8', '9', '+', '/', '4', '5', '6', '7', '8', '9', '+', '/',
'=' /* termination character */, '=' /* termination character */,
'\n', '\0' /* needed for uudecode.c */ '\0' /* needed for uudecode.c only */
}; };
const char bb_uuenc_tbl_std[65] ALIGN1 = { const char bb_uuenc_tbl_std[65] ALIGN1 = {
@ -77,7 +77,7 @@ void FAST_FUNC bb_uuencode(char *p, const void *src, int length, const char *tbl
* *
* Returns: pointer to the undecoded part of source. * Returns: pointer to the undecoded part of source.
* If points to '\0', then the source was fully decoded. * If points to '\0', then the source was fully decoded.
* (*dst): advanced past the last written byte. * (*pp_dst): advanced past the last written byte.
*/ */
const char* FAST_FUNC decode_base64(char **pp_dst, const char *src) const char* FAST_FUNC decode_base64(char **pp_dst, const char *src)
{ {
@ -85,10 +85,10 @@ const char* FAST_FUNC decode_base64(char **pp_dst, const char *src)
const char *src_tail; const char *src_tail;
while (1) { while (1) {
unsigned char translated[4]; unsigned char six_bit[4];
int count = 0; int count = 0;
/* Process one group of 4 chars */ /* Fetch up to four 6-bit values */
src_tail = src; src_tail = src;
while (count < 4) { while (count < 4) {
char *table_ptr; char *table_ptr;
@ -97,8 +97,8 @@ const char* FAST_FUNC decode_base64(char **pp_dst, const char *src)
/* Get next _valid_ character. /* Get next _valid_ character.
* bb_uuenc_tbl_base64[] contains this string: * bb_uuenc_tbl_base64[] contains this string:
* 0 1 2 3 4 5 6 * 0 1 2 3 4 5 6
* 012345678901234567890123456789012345678901234567890123456789012345 * 01234567890123456789012345678901234567890123456789012345678901234
* "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=\n" * "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
*/ */
do { do {
ch = *src; ch = *src;
@ -117,33 +117,37 @@ const char* FAST_FUNC decode_base64(char **pp_dst, const char *src)
src++; src++;
table_ptr = strchr(bb_uuenc_tbl_base64, ch); table_ptr = strchr(bb_uuenc_tbl_base64, ch);
//TODO: add BASE64_FLAG_foo to die on bad char? //TODO: add BASE64_FLAG_foo to die on bad char?
//Note that then we may need to still allow '\r' (for mail processing)
} while (!table_ptr); } while (!table_ptr);
/* Convert encoded character to decimal */ /* Convert encoded character to decimal */
ch = table_ptr - bb_uuenc_tbl_base64; ch = table_ptr - bb_uuenc_tbl_base64;
if (ch == 65) { /* '\n' */
continue;
}
/* ch is 64 if char was '=', otherwise 0..63 */ /* ch is 64 if char was '=', otherwise 0..63 */
translated[count] = ch & 63; /* 64 -> 0 */ if (ch == 64)
if (ch == 64) { /* '=' */
break; break;
} six_bit[count] = ch;
count++; count++;
} }
/* Merge 6 bit chars to 8 bit. /* Transform 6-bit values to 8-bit ones.
* count can be < 4 when we decode the tail: * count can be < 4 when we decode the tail:
* "eQ==" -> "y", not "y NUL NUL" * "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) if (count > 1)
*dst++ = translated[0] << 2 | translated[1] >> 4; *dst++ = six_bit[0] << 2 | six_bit[1] >> 4;
if (count > 2) if (count > 2)
*dst++ = translated[1] << 4 | translated[2] >> 2; *dst++ = six_bit[1] << 4 | six_bit[2] >> 2;
if (count > 3) if (count > 3)
*dst++ = translated[2] << 6 | translated[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) */ } /* while (1) */
ret: ret:
*pp_dst = dst; *pp_dst = dst;