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find_first_set_bit tweaks

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Correct sizing in m68k asm.
Make the gerneric version far more generic.

Change-Id: I32945f7431771979b3fe0da5472bdb110fd054ae
This commit is contained in:
Michael Sevakis 2012-01-27 11:47:49 -05:00
parent c6d69ae8fc
commit 74736fcfc9
2 changed files with 9 additions and 24 deletions
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29
firmware/asm/ffs.c
View file

@ -21,9 +21,7 @@
#include "config.h"
#include <inttypes.h>
/* find_first_set_bit() - this is a C version of the ffs algorithm devised
* by D.Seal and posted to comp.sys.arm on 16 Feb 1994.
*
/*
* Find the index of the least significant set bit in the word.
* return values:
* 0 - bit 0 is set
@ -32,25 +30,12 @@
* 31 - bit 31 is set
* 32 - no bits set
*/
/* Table shared with assembly code */
const uint8_t L_ffs_table[64] ICONST_ATTR =
{
/* 0 1 2 3 4 5 6 7 */
/* ----------------------------------------- */
32, 0, 1, 12, 2, 6, 0, 13, /* 0- 7 */
3, 0, 7, 0, 0, 0, 0, 14, /* 8-15 */
10, 4, 0, 0, 8, 0, 0, 25, /* 16-23 */
0, 0, 0, 0, 0, 21, 27, 15, /* 24-31 */
31, 11, 5, 0, 0, 0, 0, 0, /* 32-39 */
9, 0, 0, 24, 0, 0, 20, 26, /* 40-47 */
30, 0, 0, 0, 0, 23, 0, 19, /* 48-55 */
29, 0, 22, 18, 28, 17, 16, 0, /* 56-63 */
};
#if !defined(CPU_COLDFIRE)
int find_first_set_bit(uint32_t val)
{
return L_ffs_table[((val & -val)*0x0450fbaf) >> 26];
if (val == 0)
return 32;
/* __builtin_ffs(l(l)): Returns one plus the index of the least significant
1-bit of x, or if x is zero, returns zero. */
return __builtin_ffs(val) - 1;
}
#endif

4
firmware/asm/m68k/ffs.S
View file

@ -61,6 +61,7 @@ find_first_set_bit:
| the top 24 bits of d0 are 0 so just load the value over it
move.b (%a0, %d1.l), %d0 |
rts |
.size find_first_set_bit, .-find_first_set_bit
.section .irodata
L_ffs_table:
@ -74,5 +75,4 @@ L_ffs_table:
.byte 9, 0, 0, 24, 0, 0, 20, 26 | 40-47
.byte 30, 0, 0, 0, 0, 23, 0, 19 | 48-55
.byte 29, 0, 22, 18, 28, 17, 16, 0 | 56-63
.size find_first_set_bit, .-find_first_set_bit
.size L_ffs_table, .-L_ffs_table