diff options
| author | Michael Sevakis <jethead71@rockbox.org> | 2012-01-27 11:47:49 -0500 |
|---|---|---|
| committer | Michael Sevakis <jethead71@rockbox.org> | 2012-01-27 11:51:25 -0500 |
| commit | 74736fcfc95e786ef5aad46c73e1c53365d5d3d8 (patch) | |
| tree | 704c59443eee343e1990ddd40f6005913adae73c /firmware/asm | |
| parent | c6d69ae8fccf4e1e11fbcb55f98348d5e8f05d64 (diff) | |
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.c | 29 | ||||
| -rw-r--r-- | firmware/asm/m68k/ffs.S | 4 |
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 |