[FFmpeg-devel] [PATCH 4/4] avcodec/xbmdec: get_nibble() minor speed increase, and binary reduction
Jose Da Silva
digital at joescat.com
Mon Feb 1 05:51:10 EET 2021
Replace av_isxdigit(*ptr) and convert(*ptr) with get_nibble(*ptr) which
returns a valid nibble=={0x00..0x0f} or false==255 for all other values.
This way we only need to work with *ptr once instead of twice.
Removing inline av_isxdigit(x) functions also shrinks executable size.
Signed-off-by: Joe Da Silva <digital at joescat.com>
---
libavcodec/xbmdec.c | 42 +++++++++++++++++++++++++-----------------
1 file changed, 25 insertions(+), 17 deletions(-)
diff --git a/libavcodec/xbmdec.c b/libavcodec/xbmdec.c
index 52615dc7ab..c1fc6cb650 100644
--- a/libavcodec/xbmdec.c
+++ b/libavcodec/xbmdec.c
@@ -26,15 +26,19 @@
#include "internal.h"
#include "mathops.h"
-static int convert(uint8_t x)
+static int get_nibble(uint8_t x)
{
- if (x <= '9')
- x -= '0';
- else if (x >= 'a')
- x -= ('a' - 10);
- else
- x -= ('A' - 10);
- return x;
+ int ret = 255;
+
+ if (x <= '9') {
+ if (x >= '0')
+ ret = x - '0';
+ } else if (x >= 'a') {
+ if (x <= 'f')
+ ret = x - ('a' - 10);
+ } else if (x >= 'A' && x <= 'F')
+ ret = x - ('A' - 10);
+ return ret;
}
static int parse_str_int(const uint8_t *p, const uint8_t *end, const uint8_t *key)
@@ -94,22 +98,26 @@ static int xbm_decode_frame(AVCodecContext *avctx, void *data,
for (i = 0; i < avctx->height; i++) {
dst = p->data[0] + i * p->linesize[0];
for (j = 0; j < linesize; j++) {
- uint8_t val;
+ uint8_t nib, val;
while (ptr < end && *ptr != 'x' && *ptr != '$')
ptr++;
ptr ++;
- if (ptr < end && av_isxdigit(*ptr)) {
- val = convert(*ptr++);
- if (av_isxdigit(*ptr))
- val = (val << 4) + convert(*ptr++);
+ if (ptr < end && (val = get_nibble(*ptr)) <= 15) {
+ ptr++;
+ if ((nib = get_nibble(*ptr)) <= 15) {
+ val = (val << 4) + nib;
+ ptr++;
+ }
*dst++ = ff_reverse[val];
- if (av_isxdigit(*ptr) && j+1 < linesize) {
+ if ((val = get_nibble(*ptr)) <= 15 && j+1 < linesize) {
j++;
- val = convert(*ptr++);
- if (av_isxdigit(*ptr))
- val = (val << 4) + convert(*ptr++);
+ ptr++;
+ if ((nib = get_nibble(*ptr)) <= 15) {
+ val = (val << 4) + nib;
+ ptr++;
+ }
*dst++ = ff_reverse[val];
}
} else {
--
2.30.0
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