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Optimized base64 decode by writing 3 bytes at once.

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About 25% faster.
decode: 248852 -> 200385 decicycles
(syntax check unchanged)

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
This commit is contained in:
Reimar Döffinger 2012-01-21 22:52:56 +01:00
parent 420719e141
commit daa47fdd2c
1 changed files with 23 additions and 13 deletions
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36
libavutil/base64.c
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@ -71,37 +71,41 @@ static const uint8_t map2[256] =
#define BASE64_DEC_STEP(i) do { \ #define BASE64_DEC_STEP(i) do { \
bits = map2[in[i]]; \ bits = map2[in[i]]; \
if (bits & 0x80) \ if (bits & 0x80) \
goto out; \ goto out ## i; \
v = (v << 6) + bits; \ v = i ? (v << 6) + bits : bits; \
if (i & 3) \
*dst++ = v >> (6 - 2 * (i & 3)); \
} while(0) } while(0)
int av_base64_decode(uint8_t *out, const char *in_str, int out_size) int av_base64_decode(uint8_t *out, const char *in_str, int out_size)
{ {
int v;
uint8_t *dst = out; uint8_t *dst = out;
uint8_t *end = out + out_size; uint8_t *end = out + out_size;
// no sign extension // no sign extension
const uint8_t *in = in_str; const uint8_t *in = in_str;
unsigned bits = 0xff; unsigned bits = 0xff;
unsigned v;
v = 0; while (end - dst > 3) {
while (end - dst > 2) {
BASE64_DEC_STEP(0); BASE64_DEC_STEP(0);
BASE64_DEC_STEP(1); BASE64_DEC_STEP(1);
BASE64_DEC_STEP(2); BASE64_DEC_STEP(2);
BASE64_DEC_STEP(3); BASE64_DEC_STEP(3);
// Using AV_WB32 directly confuses compiler
v = av_be2ne32(v) >> 8;
AV_WN32(dst, v);
dst += 3;
in += 4; in += 4;
} }
if (end - dst) { if (end - dst) {
BASE64_DEC_STEP(0); BASE64_DEC_STEP(0);
BASE64_DEC_STEP(1); BASE64_DEC_STEP(1);
if (end - dst) { BASE64_DEC_STEP(2);
BASE64_DEC_STEP(2); BASE64_DEC_STEP(3);
in++; *dst++ = v >> 16;
} if (end - dst)
in += 2; *dst++ = v >> 8;
if (end - dst)
*dst++ = v;
in += 4;
} }
while (1) { while (1) {
BASE64_DEC_STEP(0); BASE64_DEC_STEP(0);
@ -114,7 +118,13 @@ int av_base64_decode(uint8_t *out, const char *in_str, int out_size)
in++; in++;
} }
out: out3:
*dst++ = v >> 10;
v <<= 2;
out2:
*dst++ = v >> 4;
out1:
out0:
return bits & 1 ? -1 : dst - out; return bits & 1 ? -1 : dst - out;
} }