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authorDenys Vlasenko2020-11-27 20:44:55 +0100
committerDenys Vlasenko2020-11-27 20:45:15 +0100
commit170b8628fabff2d81606cac052a35f8cf91cc7b2 (patch)
treec9e02294eb2d1e82966a266ad06c8312ae676b51 /libbb/uuencode.c
parentdc68a5ddac23e34fe00299d55501043bd83ae817 (diff)
downloadbusybox-170b8628fabff2d81606cac052a35f8cf91cc7b2.zip
busybox-170b8628fabff2d81606cac052a35f8cf91cc7b2.tar.gz
libbb: smaller and faster decode_base64()
function old new delta decode_base64 195 180 -15 Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'libbb/uuencode.c')
-rw-r--r--libbb/uuencode.c100
1 files changed, 36 insertions, 64 deletions
diff --git a/libbb/uuencode.c b/libbb/uuencode.c
index b4ee20c..2e9edb2 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 '\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