forked from len0rd/rockbox
5fff854126
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@8515 a1c6a512-1295-4272-9138-f99709370657
67 lines
2.9 KiB
ArmAsm
67 lines
2.9 KiB
ArmAsm
/***************************************************************************
|
|
* __________ __ ___.
|
|
* Open \______ \ ____ ____ | | _\_ |__ _______ ___
|
|
* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
|
|
* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
|
|
* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
|
|
* \/ \/ \/ \/ \/
|
|
* $Id$
|
|
*
|
|
* Copyright (C) 2006 Thom Johansen
|
|
*
|
|
* All files in this archive are subject to the GNU General Public License.
|
|
* See the file COPYING in the source tree root for full license agreement.
|
|
*
|
|
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
|
|
* KIND, either express or implied.
|
|
*
|
|
****************************************************************************/
|
|
|
|
.text
|
|
.global eq_filter
|
|
eq_filter:
|
|
ldr r12, [sp] @ get shift parameter
|
|
stmdb sp!, { r0-r11, lr } @ save all params and clobbered regs
|
|
ldmia r1!, { r4-r8 } @ load coefs
|
|
mov r10, r1 @ loop prelude expects filter struct addr in r10
|
|
|
|
.filterloop:
|
|
ldr r9, [sp] @ get pointer to this channels data
|
|
add r0, r9, #4
|
|
str r0, [sp] @ save back pointer to next channels data
|
|
ldr r9, [r9] @ r9 = x[]
|
|
ldr r14, [sp, #8] @ r14 = numsamples
|
|
ldmia r10, { r0-r3 } @ load history, r10 should be filter struct addr
|
|
str r10, [sp, #4] @ save it for loop end
|
|
.loop:
|
|
/* r0-r3 = history, r4-r8 = coefs, r9 = x[], r10..r11 = accumulator,
|
|
r12 = shift amount, r14 = number of samples.
|
|
See eq_cf.S for explanation of what this loop does. Primary difference
|
|
is the reordering of the equation we do here, which is done for register
|
|
reuse reasons, we're pretty short on regs.
|
|
*/
|
|
smull r10, r11, r6, r1 @ acc = b2*x[i - 2]
|
|
mov r1, r0 @ fix input history
|
|
smlal r10, r11, r5, r0 @ acc += b1*x[i - 1]
|
|
ldr r0, [r9] @ load input and fix history in same operation
|
|
smlal r10, r11, r4, r0 @ acc += b0*x[i]
|
|
smlal r10, r11, r7, r2 @ acc += a1*y[i - 1]
|
|
smlal r10, r11, r8, r3 @ acc += a2*y[i - 2]
|
|
mov r3, r2 @ fix output history
|
|
mov r2, r11, lsl r12 @ get result
|
|
@ TODO: arm makes it easy to mix in lower bits from r10 for extended
|
|
@ precision here, but we don't have enough regs to save the shift factor
|
|
@ we would need (32 - r12).
|
|
str r2, [r9], #4 @ save result
|
|
subs r14, r14, #1 @ are we done with this channel?
|
|
bne .loop
|
|
|
|
ldr r10, [sp, #4] @ load filter struct pointer
|
|
stmia r10!, { r0-r3 } @ save back history
|
|
ldr r11, [sp, #12] @ load number of channels
|
|
subs r11, r11, #1 @ all channels processed?
|
|
strne r11, [sp, #12]
|
|
bne .filterloop
|
|
|
|
add sp, sp, #16 @ compensate for temp storage
|
|
ldmia sp!, { r4-r11, pc }
|