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/***************************************************************************
* __________ __ ___.
* 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 }
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