base32/64: code shrink

function                                             old     new   delta
decode_base64                                        178     173      -5
decode_base32                                        217     186     -31
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-36)             Total: -36 bytes

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

1 files changed, 37 insertions, 29 deletions

diff --git a/libbb/uuencode.c b/libbb/uuencode.c
index 0e6fc8a3c..6205af261 100644
--- a/libbb/uuencode.c
+++ b/libbb/uuencode.c
@@ -92,8 +92,8 @@ const char* FAST_FUNC decode_base64(char **pp_dst, const char *src)
 {
         char *dst = *pp_dst;
         unsigned ch = 0;
+        unsigned t;
         int i = 0;
-        int t;
 
         while ((t = (unsigned char)*src) != '\0') {
                 src++;
@@ -117,11 +117,11 @@ const char* FAST_FUNC decode_base64(char **pp_dst, const char *src)
                         continue;
 
                 ch = (ch << 6) | t;
-                if (++i == 4) {
+                i = (i + 1) & 3;
+                if (i == 0) {
                         *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 "=="? */
@@ -140,9 +140,9 @@ 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;
-        uint64_t ch = 0;
+        int64_t ch = 0;
+        unsigned t;
         int i = 0;
-        int t;
 
         while ((t = (unsigned char)*src) != '\0') {
                 src++;
@@ -150,44 +150,52 @@ const char* FAST_FUNC decode_base32(char **pp_dst, const char *src)
                 /* "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
+                else {
+                        t = (t | 0x20) - 'a';
+                        if (t > 25)
 //TODO: add BASE64_FLAG_foo to die on bad char?
-                        continue;
+                                continue;
+                }
 
-                ch = (ch << 5) | (unsigned)t; /* cast prevents pointless sign-extension of t */
-                if (++i == 8) {
-                        /* testcase:
-                         * echo ' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18' | base32 | base32 -d
-                         * IOW, decoding of
-                         * EAYSAMRAGMQDIIBVEA3CANZAHAQDSIBRGAQDCMJAGEZCAMJTEAYTIIBRGUQDCNRAGE3SAMJYBI==
-                         * ====
-                         * should correctly stitch together the tail.
-                         */
-                        if (t == 0) {
-                                const char *s = src;
-                                while (*--s == '=')
-                                        t--;
-                        }
+                ch = (ch << 5) | t;
+                i = (i + 1) & 7;
+                if (i == 0) {
                         *dst++ = (char) (ch >> 32);
+                        if (src[-1] == '=') /* was last input char '='? */
+                                goto tail;
                         *dst++ = (char) (ch >> 24);
                         *dst++ = (char) (ch >> 16);
                         *dst++ = (char) (ch >> 8);
                         *dst++ = (char) ch;
-                        i = 0;
-                        if (t < 0) /* was last input char '='? */
-                                break;
                 }
         }
-        if (t < 0) /* was last input char '='? */
-                /* -t is the count of =, must be 1, 3, 4 or 6 */
-                dst -= (-t + 1) * 2 / 3; /* discard last 1, 2, 3 or 4 bytes */
         *pp_dst = dst;
         /* i is zero here if full 8-char block was decoded */
         return src - i;
+ tail:
+        {
+                const char *s = src;
+                while (*--s == '=')
+                        i++;
+                /* Why duplicate the below code? Testcase:
+                 * echo ' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18' | base32 | base32 -d
+                 * IOW, decoding of
+                 * EAYSAMRAGMQDIIBVEA3CANZAHAQDSIBRGAQDCMJAGEZCAMJTEAYTIIBRGUQDCNRAGE3SAMJYBI==
+                 * ====
+                 * must correctly stitch together the tail, must not overwrite
+                 * the tail before it is analyzed! (we can be decoding in-place)
+                 * Else testcase fails, prints trailing extra NUL bytes.
+                 */
+                *dst++ = (char) (ch >> 24);
+                *dst++ = (char) (ch >> 16);
+                *dst++ = (char) (ch >> 8);
+                *dst++ = (char) ch;
+                dst -= (i+1) * 2 / 3; /* discard last 1, 2, 3 or 4 bytes */
+        }
+        *pp_dst = dst;
+        return src;
 }
 #endif