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af_pan: comment a tricky piece of code.

This commit is contained in:
Nicolas George 2012-02-15 19:41:41 +01:00
parent cba4e2cbbc
commit bd5080b1b0
1 changed files with 4 additions and 0 deletions
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4
libavfilter/af_pan.c
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@ -64,14 +64,17 @@ static int parse_channel_name(char **arg, int *rchannel, int *rnamed)
int len, i, channel_id = 0; int len, i, channel_id = 0;
int64_t layout, layout0; int64_t layout, layout0;
/* try to parse a channel name, e.g. "FL" */
if (sscanf(*arg, " %7[A-Z] %n", buf, &len)) { if (sscanf(*arg, " %7[A-Z] %n", buf, &len)) {
layout0 = layout = av_get_channel_layout(buf); layout0 = layout = av_get_channel_layout(buf);
/* channel_id <- first set bit in layout */
for (i = 32; i > 0; i >>= 1) { for (i = 32; i > 0; i >>= 1) {
if (layout >= (int64_t)1 << i) { if (layout >= (int64_t)1 << i) {
channel_id += i; channel_id += i;
layout >>= i; layout >>= i;
} }
} }
/* reject layouts that are not a single channel */
if (channel_id >= MAX_CHANNELS || layout0 != (int64_t)1 << channel_id) if (channel_id >= MAX_CHANNELS || layout0 != (int64_t)1 << channel_id)
return AVERROR(EINVAL); return AVERROR(EINVAL);
*rchannel = channel_id; *rchannel = channel_id;
@ -79,6 +82,7 @@ static int parse_channel_name(char **arg, int *rchannel, int *rnamed)
*arg += len; *arg += len;
return 0; return 0;
} }
/* try to parse a channel number, e.g. "c2" */
if (sscanf(*arg, " c%d %n", &channel_id, &len) && if (sscanf(*arg, " c%d %n", &channel_id, &len) &&
channel_id >= 0 && channel_id < MAX_CHANNELS) { channel_id >= 0 && channel_id < MAX_CHANNELS) {
*rchannel = channel_id; *rchannel = channel_id;