2cd37d65e
Denys Vlasenko
2020-11-27
Subject
libbb: faster and smaller decode_base32()
Binary
No binary (build failed)
Architecture & Compiler Flags
—
Build Log
(log yok)
Commit Diff GitHub →
libbb/uuencode.c+34 -50
| @@ -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; |
| - | |
| - | while (1) { |
| - | unsigned char five_bit[8]; |
| - | int count = 0; |
| - | |
| - | /* Fetch up to eight 5-bit values */ |
| - | src_tail = src; |
| - | while (count < 8) { |
| - | char *table_ptr; |
| - | int ch; |
| + | uint64_t ch = 0; |
| + | int i = 0; |
| - | /* 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); |
| + | while (*src) { |
| + | int t = (unsigned char)*src++; |
| - | /* Convert encoded character to decimal */ |
| - | ch = table_ptr - bb_uuenc_tbl_base32; |
| + | /* "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; |
| - | /* 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 | |