libbb: faster and smaller decode_base32()

function                                             old     new   delta
decode_base32                                        275     224     -51

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 34 insertions, 50 deletions

diff --git a/libbb/uuencode.c b/libbb/uuencode.c
index 2e9edb219..7c7f1cf1c 100644
--- a/libbb/uuencode.c
+++ b/libbb/uuencode.c
@@ -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