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authorMichael Sevakis <jethead71@rockbox.org>2012-01-27 11:47:49 -0500
committerMichael Sevakis <jethead71@rockbox.org>2012-01-27 11:51:25 -0500
commit74736fcfc95e786ef5aad46c73e1c53365d5d3d8 (patch)
tree704c59443eee343e1990ddd40f6005913adae73c /firmware/asm
parentc6d69ae8fccf4e1e11fbcb55f98348d5e8f05d64 (diff)
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find_first_set_bit tweaks
Correct sizing in m68k asm. Make the gerneric version far more generic. Change-Id: I32945f7431771979b3fe0da5472bdb110fd054ae
Diffstat (limited to 'firmware/asm')
-rw-r--r--firmware/asm/ffs.c29
-rw-r--r--firmware/asm/m68k/ffs.S4
2 files changed, 9 insertions, 24 deletions
diff --git a/firmware/asm/ffs.c b/firmware/asm/ffs.c
index f68a9cef8c..6826f42e94 100644
--- a/firmware/asm/ffs.c
+++ b/firmware/asm/ffs.c
@@ -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
diff --git a/firmware/asm/m68k/ffs.S b/firmware/asm/m68k/ffs.S
index 2a39ae5bcd..87421ffe10 100644
--- a/firmware/asm/m68k/ffs.S
+++ b/firmware/asm/m68k/ffs.S
@@ -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