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Invert divisor earlier in udiv32_arm, allowing the div0 test to be done before entering the 32-bit divide portion of the code, and making the handling of div0 simpler.

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@24166 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Andrew Mahone 2010-01-03 15:57:03 +00:00
parent 6fef14bd16
commit 5313bf52b5
1 changed files with 24 additions and 36 deletions
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60
apps/codecs/lib/udiv32_armv4.S
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@ -44,23 +44,21 @@
has the high bit set, this is fine, everything inside .rept will be
skipped, and the add before and adcs after will set the one-bit result
to zero. */
cmp \divisor, \dividend, lsr #16
movls \divisor, \divisor, lsl #16
addls \bits, \bits, #16
cmp \divisor, \dividend, lsr #8
movls \divisor, \divisor, lsl #8
addls \bits, \bits, #8
cmp \divisor, \dividend, lsr #4
movls \divisor, \divisor, lsl #4
addls \bits, \bits, #4
cmp \divisor, \dividend, lsr #2
movls \divisor, \divisor, lsl #2
addls \bits, \bits, #2
cmp \divisor, \dividend, lsr #1
movls \divisor, \divisor, lsl #1
addls \bits, \bits, #1
rsbs \divisor, \divisor, #0
bcs .L_div0
cmn \divisor, \dividend, lsr #16
movcs \divisor, \divisor, lsl #16
addcs \bits, \bits, #16
cmn \divisor, \dividend, lsr #8
movcs \divisor, \divisor, lsl #8
addcs \bits, \bits, #8
cmn \divisor, \dividend, lsr #4
movcs \divisor, \divisor, lsl #4
addcs \bits, \bits, #4
cmn \divisor, \dividend, lsr #2
movcs \divisor, \divisor, lsl #2
addcs \bits, \bits, #2
cmn \divisor, \dividend, lsr #1
movcs \divisor, \divisor, lsl #1
addcs \bits, \bits, #1
adds \result, \dividend, \divisor
subcc \result, \result, \divisor
rsb \curbit, \bits, #31
@ -88,6 +86,13 @@
.type udiv32_arm,%function
udiv32_arm:
/* Invert divisor. ARM_DIV_31_BODY uses adc to both subtract the divisor
and add the next bit of the result. The correction code at .L_udiv32
does not need the divisor inverted, but can be modified to work with it,
and this allows the zero divisor test to be done early and without an
explicit comparison. */
rsbs r1, r1, #0
beq .L_div0
tst r0, r0
/* High bit must be unset, otherwise shift numerator right, calculate,
and correct results. As this case is very uncommon we want to avoid
@ -106,9 +111,6 @@ udiv32_arm:
address. */
mov r0, r0, lsr #1
bl .L_udiv31
/* This address is never a branch target, but is used to test lr before
calling __div0. */
.L_udiv32_div0_trap:
ldmdb sp, { r2, r3, lr }
/* Move the low bit of the original numerator to the carry bit */
movs r2, r2, lsr #1
@ -116,26 +118,12 @@ udiv32_arm:
adc r1, r1, r1
/* Subtract the original divisor from the remainder, setting carry if the
result is non-negative */
subs r1, r1, r3
adds r1, r1, r3
/* Shift quotient left one and add carry bit */
adc r0, r0, r0
bx lr
.L_div0:
/* Check the return address, since .L_udiv32 uses bl to wrap the 31-bit
divider. If the return address is at .L_udiv32_div0_trap, then the
the return address of the original caller is at sp - 4
*/
adr r2, .L_udiv32_div0_trap
cmp r2, lr
subeq sp, sp, #4
#if defined(__ARM_EABI__) || !defined(USE_IRAM)
bleq __div0
#else
ldr r3, =__div0
moveq lr, pc
bxeq r3
#endif
/* Otherwise, push lr to the stack before calling __div0 */
/* __div0 expects the calling address on the top of the stack */
stmdb sp!, { lr }
#if defined(__ARM_EABI__) || !defined(USE_IRAM)
bl __div0