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Merge pull request #223 from gwilymk/tiny-audio-optimisation

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Tiny audio optimisation
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Gwilym Kuiper 2022-04-26 22:18:57 +01:00 committed by GitHub
parent 0e7fb41501 0761132779
commit 9cd3d7440d
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1 changed files with 43 additions and 16 deletions
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59
agb/src/sound/mixer/mixer.s
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@ -152,39 +152,66 @@ agb_arm_func agb_rs__mixer_add_stereo
agb_arm_end agb_rs__mixer_add_stereo
.macro clamp_s8 reg:req
cmn \reg, #127
mvnlt \reg, #127
cmn \reg, #128
mvnlt \reg, #128
cmp \reg, #128
movgt \reg, #128
cmp \reg, #127
movgt \reg, #127
.endm
agb_arm_func agb_rs__mixer_collapse
@ Arguments:
@ r0 = target buffer (i8)
@ r1 = input buffer (i16) of fixnums with 4 bits of precision (read in sets of i16 in an i32)
push {r4}
push {r4, r5, r6, r7, r8, r9, r10}
ldr r2, agb_rs__buffer_size @ loop counter
mov r4, r2
1:
@ r12 = *r1; r1++
ldr r12, [r1], #4
.macro load_sample left_reg:req right_reg:req
@ left_reg = *r1; r1++
ldr \left_reg, [r1], #4
lsl r3, r12, #16 @ r3 is going to be the right sample, push r12 left 16 bits first
asr r3, r3, #20 @ move r3 back to being the correct value
mov r12, r12, asr #20 @ r12 = left sample
lsl \right_reg, \left_reg, #16 @ push the sample 16 bits first
asr \right_reg, \right_reg, #20 @ move right sample back to being the correct value
mov \left_reg, \left_reg, asr #20 @ now we only have the left sample
clamp_s8 r12 @ clamp the audio to 8 bit values
clamp_s8 r3
clamp_s8 \left_reg @ clamp the audio to 8 bit values
clamp_s8 \right_reg
.endm
strb r3, [r0, r4] @ *(r0 + r4 = SOUND_BUFFER_SIZE) = r3
strb r12, [r0], #1 @ *r0 = r12; r0++
load_sample r3, r12
load_sample r5, r6
load_sample r7, r8
load_sample r9, r10
subs r2, r2, #1 @ r2 -= 1
@ combine the four samples so we can store in 32-bit chunks
@ need to ensure that we don't overwrite the extra bit of the sample
and r3, r3, #255
and r12, r12, #255
and r5, r5, #255
and r6, r6, #255
and r7, r7, #255
and r8, r8, #255
and r9, r9, #255
and r10, r10, #255
@ combine all of the samples
orr r3, r3, r5, lsl #8
orr r3, r3, r7, lsl #16
orr r3, r3, r9, lsl #24
orr r12, r12, r6, lsl #8
orr r12, r12, r8, lsl #16
orr r12, r12, r10, lsl #24
str r3, [r0, r4] @ *(r0 + (r4 = SOUND_BUFFER_SIZE)) = r3
str r12, [r0], #4 @ *r0 = r12; r0 += 4
subs r2, r2, #4 @ r2 -= 4
bne 1b @ loop if not 0
pop {r4}
pop {r4, r5, r6, r7, r8, r9, r10}
bx lr
agb_arm_end agb_rs__mixer_collapse