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Diffstat (limited to 'firmware/target/coldfire/ffs-coldfire.S')
| -rw-r--r-- | firmware/target/coldfire/ffs-coldfire.S | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/firmware/target/coldfire/ffs-coldfire.S b/firmware/target/coldfire/ffs-coldfire.S new file mode 100644 index 0000000000..4f21013123 --- /dev/null +++ b/firmware/target/coldfire/ffs-coldfire.S | |||
| @@ -0,0 +1,62 @@ | |||
| 1 | /*************************************************************************** | ||
| 2 | * __________ __ ___. | ||
| 3 | * Open \______ \ ____ ____ | | _\_ |__ _______ ___ | ||
| 4 | * Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ / | ||
| 5 | * Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < < | ||
| 6 | * Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \ | ||
| 7 | * \/ \/ \/ \/ \/ | ||
| 8 | * $Id$ | ||
| 9 | * | ||
| 10 | * Copyright (C) 2008 by Michael Sevakis | ||
| 11 | * | ||
| 12 | * All files in this archive are subject to the GNU General Public License. | ||
| 13 | * See the file COPYING in the source tree root for full license agreement. | ||
| 14 | * | ||
| 15 | * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY | ||
| 16 | * KIND, either express or implied. | ||
| 17 | * | ||
| 18 | ****************************************************************************/ | ||
| 19 | #include "config.h" | ||
| 20 | |||
| 21 | /**************************************************************************** | ||
| 22 | * int find_first_set_bit(uint32_t val); | ||
| 23 | * | ||
| 24 | * Find the index of the least significant set bit in the 32-bit word. | ||
| 25 | * | ||
| 26 | * return values: | ||
| 27 | * 0 - bit 0 is set | ||
| 28 | * 1 - bit 1 is set | ||
| 29 | * ... | ||
| 30 | * 31 - bit 31 is set | ||
| 31 | * 32 - no bits set | ||
| 32 | ****************************************************************************/ | ||
| 33 | .text | ||
| 34 | .align 2 | ||
| 35 | .global find_first_set_bit | ||
| 36 | .type find_first_set_bit,@function | ||
| 37 | find_first_set_bit: | ||
| 38 | | this is a coldfire version of the ffs algorithm devised by D.Seal | ||
| 39 | | and posted to comp.sys.arm on 16 Feb 1994. | ||
| 40 | | | ||
| 41 | | Output modified to suit rockbox purposes. | ||
| 42 | |||
| 43 | | Standard trick to isolate bottom bit in r0 or 0 if r0 = 0 on entry | ||
| 44 | move.l 4(%sp), %d1 | %d1 = %d1 & -%d1 | ||
| 45 | lea.l L_ffs_table, %a0 | %a0 = table address | ||
| 46 | move.l %d1, %d0 | | ||
| 47 | neg.l %d1 | | ||
| 48 | and.l %d0, %d1 | | ||
| 49 | |||
| 50 | | now %d1 has at most one set bit, call this X | ||
| 51 | |||
| 52 | move.l #0x0450fbaf, %d0 | %d0 = multiplier | ||
| 53 | mulu.l %d0, %d1 | %d1 = X * 0x0450fbaf | ||
| 54 | |||
| 55 | | now lookup in table indexed on top 6 bits of %d0 | ||
| 56 | moveq.l #26, %d0 | %d0 = final shift count | ||
| 57 | lsr.l %d0, %d1 | | ||
| 58 | clr.l %d0 | | ||
| 59 | move.b (%a0, %d1.l), %d0 | | ||
| 60 | rts | | ||
| 61 | |||
| 62 | .size find_first_set_bit, .-find_first_set_bit | ||