e6094d95b
Denys Vlasenko
2011-10-28
Subject
libbb: shrink base64 decoding a bit
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libbb/uuencode.c+23 -19
| @@ -10,7 +10,7 @@ | |
| #include "libbb.h" | |
| /* 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', | |
| 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', | |
| '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', | |
| '4', '5', '6', '7', '8', '9', '+', '/', | |
| '=' /* termination character */, | |
| - | '\n', '\0' /* needed for uudecode.c */ |
| + | '\0' /* needed for uudecode.c only */ |
| }; | |
| 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. | |
| * 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) | |
| { | |
| @@ -85,10 +85,10 @@ const char* FAST_FUNC decode_base64(char **pp_dst, const char *src) | |
| const char *src_tail; | |
| while (1) { | |
| - | unsigned char translated[4]; |
| + | unsigned char six_bit[4]; |
| int count = 0; | |
| - | /* Process one group of 4 chars */ |
| + | /* Fetch up to four 6-bit values */ |
| src_tail = src; | |
| while (count < 4) { | |
| char *table_ptr; | |
| @@ -97,8 +97,8 @@ const char* FAST_FUNC decode_base64(char **pp_dst, const char *src) | |
| /* Get next _valid_ character. | |
| * bb_uuenc_tbl_base64[] contains this string: | |
| * 0 1 2 3 4 5 6 | |
| - | * 012345678901234567890123456789012345678901234567890123456789012345 |
| - | * "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=\n" |
| + | * 01234567890123456789012345678901234567890123456789012345678901234 |
| + | * "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=" |
| */ | |
| do { | |
| ch = *src; | |
| @@ -117,33 +117,37 @@ const char* FAST_FUNC decode_base64(char **pp_dst, const char *src) | |
| src++; | |
| table_ptr = strchr(bb_uuenc_tbl_base64, ch); | |
| //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); | |
| /* Convert encoded character to decimal */ | |
| ch = table_ptr - bb_uuenc_tbl_base64; | |
| - | if (ch == 65) { /* '\n' */ |
| - | continue; |
| - | } |
| /* ch is 64 if char was '=', otherwise 0..63 */ | |
| - | translated[count] = ch & 63; /* 64 -> 0 */ |
| - | if (ch == 64) { /* '=' */ |
| + | if (ch == 64) |
| break; | |
| - | } |
| + | six_bit[count] = ch; |
| 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: | |
| - | * "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) | |
| - | *dst++ = translated[0] << 2 | translated[1] >> 4; |
| + | *dst++ = six_bit[0] << 2 | six_bit[1] >> 4; |
| if (count > 2) | |
| - | *dst++ = translated[1] << 4 | translated[2] >> 2; |
| + | *dst++ = six_bit[1] << 4 | six_bit[2] >> 2; |
| 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) */ | |
| ret: | |
| *pp_dst = dst; | |