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Add ffsl(), ffsll(), fls(), flsl(), flsll() and use GCC's __builtin_ctz/__builtin_clz for faster implementation of these

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This commit is contained in:
Jussi Kivilinna
2017-03-24 09:41:31 -06:00
committed by Gregory Nutt
parent 61ff3c6b84
commit d0c54039dc
9 changed files with 508 additions and 4 deletions
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libc/string/lib_ffs.c
+9 -3
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@@ -33,11 +33,11 @@
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/compiler.h>
#include <strings.h>
/****************************************************************************
@@ -55,11 +55,11 @@
*
* Description:
* The ffs() function will find the first bit set (beginning with the least
* significant bit) in i, and return the index of that bit. Bits are
* significant bit) in j, and return the index of that bit. Bits are
* numbered starting at one (the least significant bit).
*
* Returned Value:
* The ffs() function will return the index of the first bit set. If i is
* The ffs() function will return the index of the first bit set. If j is
* 0, then ffs() will return 0.
*
****************************************************************************/
@@ -70,6 +70,11 @@ int ffs(int j)
if (j != 0)
{
#ifdef CONFIG_HAVE_BUILTIN_CTZ
/* Count trailing zeros function can be used to implement ffs. */
ret = __builtin_ctz(j) + 1;
#else
unsigned int value = (unsigned int)j;
int bitno;
@@ -81,6 +86,7 @@ int ffs(int j)
break;
}
}
#endif
}
return ret;