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utils: factor out the leading zero count code

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This commit is contained in:
Wim Taymans 2009-08-28 12:33:37 +02:00
parent 2b8d7a54cc
commit 0ef7a5af52
1 changed files with 21 additions and 10 deletions
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31
gst/gstutils.c
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@ -247,6 +247,26 @@ gst_util_uint64_mul_uint64 (GstUInt64 * c1, GstUInt64 * c0, guint64 arg1,
c1->ll = (guint64) v.l.high * n.l.high + c1->l.high + a1.l.high + b0.l.high;
}
/* count leading zeros */
static guint
gst_util_clz (guint32 val)
{
guint s;
s = val | (val >> 1);
s |= (s >> 2);
s |= (s >> 4);
s |= (s >> 8);
s = ~(s | (s >> 16));
s = s - ((s >> 1) & 0x55555555);
s = (s & 0x33333333) + ((s >> 2) & 0x33333333);
s = (s + (s >> 4)) & 0x0f0f0f0f;
s += (s >> 8);
s = (s + (s >> 16)) & 0x3f;
return s;
}
/* based on Hacker's Delight p152 */
static guint64
gst_util_div128_64 (GstUInt64 c1, GstUInt64 c0, guint64 denom)
@ -259,16 +279,7 @@ gst_util_div128_64 (GstUInt64 c1, GstUInt64 c0, guint64 denom)
/* count number of leading zeroes, we know they must be in the high
* part of denom since denom > G_MAXUINT32. */
s = v.l.high | (v.l.high >> 1);
s |= (s >> 2);
s |= (s >> 4);
s |= (s >> 8);
s = ~(s | (s >> 16));
s = s - ((s >> 1) & 0x55555555);
s = (s & 0x33333333) + ((s >> 2) & 0x33333333);
s = (s + (s >> 4)) & 0x0f0f0f0f;
s += (s >> 8);
s = (s + (s >> 16)) & 0x3f;
s = gst_util_clz (v.l.high);
if (s > 0) {
/* normalize divisor and dividend */