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use SIMDE intrinsic to count leading zeroes and make rounding exact

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This commit is contained in:
Thomas Schlichter
2024-09-23 17:58:03 +02:00
committed by francescomani
parent d304865489
commit 4e09353b43
1 changed files with 18 additions and 18 deletions
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openair1/PHY/TOOLS/log2_approx.c
+18 -18
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@@ -19,18 +19,19 @@
* contact@openairinterface.org
*/
#include <simde/x86/avx512/lzcnt.h>
unsigned char log2_approx(unsigned int x)
{
unsigned char l2 = 0;
unsigned int tmp = x >> 1;
const unsigned int round_val = 3037000499U; // 2^31.5
if (!x)
return 0;
while (tmp) {
l2++;
tmp >>= 1;
}
if (l2)
l2 += (x >> (l2 - 1)) & 1;
int l2 = simde_x_clz32(x);
if (x > (round_val >> l2))
l2 = 32 - l2;
else
l2 = 31 - l2;
return l2;
}
@@ -50,16 +51,15 @@ unsigned char factor2(unsigned int x)
unsigned char log2_approx64(unsigned long long int x)
{
unsigned char l2 = 0;
unsigned long long int tmp = x >> 1;
const unsigned long long round_val = 13043817825332782212ULL; // 2^63.5
if (!x)
return 0;
while (tmp) {
l2++;
tmp >>= 1;
}
if (l2)
l2 += (x >> (l2 - 1)) & 1;
int l2 = simde_x_clz64(x);
if (x > (round_val >> l2))
l2 = 64 - l2;
else
l2 = 63 - l2;
return l2;
}