112 lines
3.6 KiB
ArmAsm
112 lines
3.6 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) 2019 Franklin Wei
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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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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/*
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* Sound mixing code for ARM.
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*
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* Takes an array of 8-bit mono audio and outputs stereo 16-bit
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* samples. Stereo volumes are passed as arguments r0 and r1.
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*
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* Bear with me. This is my first ARM assembly, ever.
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*/
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.text
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.align 2
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.global SND_PaintChannelFrom8
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.type SND_PaintChannelFrom8, %function
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#if defined(__ARM_ARCH_5TEJ__)
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SND_PaintChannelFrom8:
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;; r0: int true_lvol
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;; r1: int true_rvol
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;; r2: char *sfx
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;; r3: int count
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stmfd sp!, {r4, r5, r6, r7, r8, sl}
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ldr ip, =paintbuffer
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ldr ip, [ip]
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mov r0, r0, asl #16 ; prescale by 2^16
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mov r1, r1, asl #16
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sub r3, r3, #1 ; count backwards
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ldrh sl, =0xffff ; halfword mask
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1:
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ldrsb r4, [r2, r3] ; load input sample
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ldr r8, [ip, r3, lsl #2] ; load output sample pair from paintbuffer
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; (left:right in memory -> right:left in register)
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;; right channel (high half)
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mul r5, r4, r1 ; scaledright = sfx[i] * (true_rvol << 16) -- bottom half is zero
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qadd r7, r5, r8 ; right = scaledright + right (in high half of word)
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bic r7, r7, sl ; zero bottom half of r7
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;; left channel (low half)
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mul r5, r4, r0 ; scaledleft = sfx[i] * (true_rvol << 16)
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mov r8, r8, lsl #16 ; extract original left channel from paintbuffer
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qadd r8, r5, r8 ; left = scaledleft + left
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orr r7, r7, r8, lsr #16 ; combine right:left in r7
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str r7, [ip, r3, lsl #2] ; write right:left to output buffer
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subs r3, r3, #1
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bgt 1b ; must use bgt instead of bne in case count=1
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ldmfd sp!, {r4, r5, r6, r7, r8, sl}
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bx lr
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#elif defined(__ARM_ARCH_6__) ; ARMv6 with QADD16 (disabled)
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SND_PaintChannelFrom8:
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;; r0: int true_lvol
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;; r1: int true_rvol
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;; r2: char *sfx
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;; r3: int count
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stmfd sp!, {r4, r5, r6, r7}
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ldr ip, =paintbuffer
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ldr ip, [ip] ; load paintbuffer address
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sub r3, r3, #1 ; we'll count backwards
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1:
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ldrsb r4, [r2, r3] ; load sfx[i] -> r4
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ldr r7, [ip, r3, lsl #2] ; load old sample pair
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mul r5, r4, r1 ; SCALEDRIGHT = SFXI * true_rvol
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mul r6, r4, r0 ; SCALEDLEFT = SFXI * true_rvol
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orr r6, r6, r5, lsl #16 ; combine samples as 32-bit
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qadd16 r6, r6, r7 ; parallel 16-bit add
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str r6, [ip, r3, lsl #2] ; write 32-bit to paintbuffer
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subs r3, r3, #1
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bgt 1b
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ldmfd sp!, {r4, r5, r6, r7}
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bx lr
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#else
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#error ARMv5/6 only
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#endif
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