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Extract a macro for this

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This commit is contained in:
Gwilym Inzani 2023-06-16 22:15:45 +01:00
parent 6cf3ecaf36
commit 9e08303e62
1 changed files with 12 additions and 7 deletions
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19
agb/src/sound/mixer/mixer.s
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@ -98,17 +98,15 @@ agb_arm_func agb_rs__mixer_add_stereo
@ r2 - volume to play the sound at
@
@ The sound buffer must be SOUND_BUFFER_SIZE * 2 in size = 176 * 2
push {{r4-r9}}
push {{r4-r12}}
ldr r5, =0x00000FFF
ldr r8, =agb_rs__buffer_size
ldr r8, [r8]
1:
.rept 4
ldrsh r6, [r0], #2 @ load the current sound sample to r6
ldr r4, [r1] @ read the current value
.macro add_stereo_sample sample_reg:req
ldrsh r6, [r0], #2 @ load the current sound sample to r6
@ This is slightly convoluted, but is mainly done for performance reasons. It is better
@ to hit ROM just once and then do 3 really simple instructions then do 2 ldrsbs however annoying
@ -129,7 +127,14 @@ agb_arm_func agb_rs__mixer_add_stereo
lsl r6, r6, #24 @ r6 = | R | 0 | 0 | 0 | drop everything except the right sample
orr r6, r7, r6, asr #8 @ r6 = | 1 | R | 1 | L | now we have it perfectly set up
mla r4, r6, r2, r4 @ r4 += r6 * r2 (calculating both the left and right samples together)
mla \sample_reg, r6, r2, \sample_reg @ r4 += r6 * r2 (calculating both the left and right samples together)
.endm
1:
.rept 4
ldr r4, [r1] @ read the current value
add_stereo_sample r4
str r4, [r1], #4 @ store the new value, and increment the pointer
.endr
@ -137,7 +142,7 @@ agb_arm_func agb_rs__mixer_add_stereo
subs r8, r8, #4 @ loop counter
bne 1b @ jump back if we're done with the loop
pop {{r4-r9}}
pop {{r4-r12}}
bx lr
agb_arm_end agb_rs__mixer_add_stereo