10a22849e6
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@12454 a1c6a512-1295-4272-9138-f99709370657
89 lines
3.7 KiB
ArmAsm
89 lines
3.7 KiB
ArmAsm
/***************************************************************************
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* __________ __ ___.
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* Open \______ \ ____ ____ | | _\_ |__ _______ ___
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* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
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* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
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* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
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* \/ \/ \/ \/ \/
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* $Id$
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*
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* Copyright (C) 2006-2007 Thom Johansen
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*
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* All files in this archive are subject to the GNU General Public License.
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* See the file COPYING in the source tree root for full license agreement.
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*
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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* KIND, either express or implied.
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*
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****************************************************************************/
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/* uncomment this to make filtering calculate lower bits after shifting.
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* without this, "shift" - 1 of the lower bits will be lost here.
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*/
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/* #define HIGH_PRECISION */
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/*
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* void eq_filter(int32_t **x, struct eqfilter *f, unsigned num,
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* unsigned channels, unsigned shift)
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*/
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.text
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.global eq_filter
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eq_filter:
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lea.l (-11*4, %sp), %sp
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movem.l %d2-%d7/%a2-%a6, (%sp) | save clobbered regs
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move.l (11*4+8, %sp), %a5 | fetch filter structure address
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move.l (11*4+20, %sp), %d7 | load shift count
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subq.l #1, %d7 | EMAC gives us one free shift
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#ifdef HIGH_PRECISION
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moveq.l #8, %d6
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sub.l %d7, %d6 | shift for lower part of accumulator
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#endif
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movem.l (%a5), %a0-%a4 | load coefs
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lea.l (5*4, %a5), %a5 | point to filter history
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.filterloop:
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move.l (11*4+4, %sp), %a6 | load input channel pointer
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addq.l #4, (11*4+4, %sp) | point x to next channel
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move.l (%a6), %a6
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move.l (11*4+12, %sp), %d5 | number of samples
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movem.l (%a5), %d0-%d3 | load filter history
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/* d0-d3 = history, d4 = temp, d5 = sample count, d6 = lower shift amount,
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* d7 = upper shift amount, a0-a4 = coefs, a5 = history pointer, a6 = x[]
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*/
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.loop:
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/* Direct form 1 filtering code. We assume DSP has put EMAC in frac mode.
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* y[n] = b0*x[i] + b1*x[i - 1] + b2*x[i - 2] + a1*y[i - 1] + a2*y[i - 2],
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* where y[] is output and x[] is input. This is performed out of order
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* to do parallel load of input value.
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*/
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mac.l %a2, %d1, %acc0 | acc = b2*x[i - 2]
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move.l %d0, %d1 | fix input history
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mac.l %a1, %d0, (%a6), %d0, %acc0 | acc += b1*x[i - 1], x[i] -> d0
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mac.l %a0, %d0, %acc0 | acc += b0*x[i]
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mac.l %a3, %d2, %acc0 | acc += a1*y[i - 1]
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mac.l %a4, %d3, %acc0 | acc += a2*y[i - 2]
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move.l %d2, %d3 | fix output history
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#ifdef HIGH_PRECISION
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move.l %accext01, %d2 | fetch lower part of accumulator
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move.b %d2, %d4 | clear upper three bytes
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lsr.l %d6, %d4 | shift lower bits
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#endif
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movclr.l %acc0, %d2 | fetch upper part of result
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asl.l %d7, %d2 | restore fixed point format
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#ifdef HIGH_PRECISION
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or.l %d2, %d4 | combine lower and upper parts
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#endif
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move.l %d2, (%a6)+ | save result
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subq.l #1, %d5 | are we done with this channel?
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jne .loop
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movem.l %d0-%d3, (%a5) | save history back to struct
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lea.l (4*4, %a5), %a5 | point to next channel's history
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subq.l #1, (11*4+16, %sp) | have we processed both channels?
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jne .filterloop
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movem.l (%sp), %d2-%d7/%a2-%a6
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lea.l (11*4, %sp), %sp
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rts
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