170b8628f
Denys Vlasenko
2020-11-27
Subject
libbb: smaller and faster decode_base64()
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libbb/uuencode.c+36 -64
| @@ -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; |
| - | |
| - | while (1) { |
| - | unsigned char six_bit[4]; |
| - | int count = 0; |
| + | unsigned ch = 0; |
| + | int i = 0; |
| - | /* Fetch up to four 6-bit values */ |
| - | src_tail = src; |
| - | while (count < 4) { |
| - | char *table_ptr; |
| - | int ch; |
| + | while (*src) { |
| + | int t = (unsigned char)*src++; |
| - | /* 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); |
| - | |
| - | /* Convert encoded character to decimal */ |
| - | ch = table_ptr - bb_uuenc_tbl_base64; |
| + | continue; |
| - | /* 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++; |
| + | } |
| + | ch = 0; |
| } | |
| - | |
| - | /* 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: |
| + | } |
| *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 | |
networking/httpd.c+0 -37
| @@ -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 | |