1. ffmpeg
  2. Commit 523f676b51d8a2eaeb7d75ccdb0258d271430430
Browse code

Use a full table for base64 decode.

Also encodes error or end marker into table.
About 20% faster.
decode: 466491 -> 374139 decicycles
syntax check: 236955 -> 161182 decicycles

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

Reimar Döffinger authored on 2012/01/21 20:22:19
Showing 1 changed files
libavutil/base64.c
History View file @ 523f676
... ... 
@@ -30,32 +30,59 @@
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 #include "intreadwrite.h"
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 /* ---------------- private code */
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-static const uint8_t map2[] =
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+static const uint8_t map2[256] =
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 {
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+    0xfe, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff,
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+
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     0x3e, 0xff, 0xff, 0xff, 0x3f, 0x34, 0x35, 0x36,
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     0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0xff,
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-    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x00, 0x01,
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+    0xff, 0xff, 0xfe, 0xff, 0xff, 0xff, 0x00, 0x01,
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     0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09,
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     0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x10, 0x11,
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     0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19,
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     0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1a, 0x1b,
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     0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23,
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     0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b,
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-    0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33
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+    0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33,
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+
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+                      0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
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 };
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-int av_base64_decode(uint8_t *out, const char *in, int out_size)
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+int av_base64_decode(uint8_t *out, const char *in_str, int out_size)
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 {
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     int i, v;
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     uint8_t *dst = out;
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     uint8_t *end = out + out_size;
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+    // no sign extension
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+    const uint8_t *in = in_str;
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     v = 0;
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     for (i = 0; ; i++) {
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-        unsigned int index= in[i]-43;
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-        if (index>=FF_ARRAY_ELEMS(map2) || map2[index] == 0xff)
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-            return in[i] && in[i] != '=' ? -1 : dst - out;
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-        v = (v << 6) + map2[index];
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+        unsigned bits = map2[in[i]];
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+        if (bits & 0x80)
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+            return bits & 1 ? -1 : dst - out;
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+        v = (v << 6) + bits;
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         if (i & 3) {
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             if (dst < end) {
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                 *dst++ = v >> (6 - 2 * (i & 3));