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reuse r4

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This commit is contained in:
Gwilym Kuiper 2021-08-01 20:59:01 +01:00
parent 18d96e4349
commit 2db696f8bf
1 changed files with 9 additions and 3 deletions
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12
agb/src/sound/mixer/mixer.s
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@ -23,15 +23,21 @@ agb_rs__mixer_add:
mov r5, #0 @ current index we're reading from
@ kept between iterations:
@ r12 - current write offset into the output buffer (r1)
@ r8 - the constant 352
@ r5 - the current index from the input buffer we're reading from (r0)
@ all other registers are temporary
1:
add r4, r0, r5, asr #8 @ calculate the address of the next read form the sound buffer
add r5, r5, r2 @ calculate the position to read the next step from
ldrsb r10, [r4] @ load the current value we want to read
add r5, r5, r2 @ calculate the position to read the next step from
mov r6, r1 @ r6 = current buffer location
ldrh r9, [r6, r12]! @ load the current buffer value (r12 being the offset) but pre-increment r6 by r12
mla r7, r10, r3, r9 @ r7 = r10 * r3 + r9 = current sound value * left amount + previous buffer value
ldrh r4, [r6, r12]! @ load the current buffer value (r12 being the offset) but pre-increment r6 by r12
mla r7, r10, r3, r4 @ r7 = r10 * r3 + r9 = current sound value * left amount + previous buffer value
strh r7, [r6], r8 @ *r6 = r7, r6 += r8 where r8 = 352 = offset for the right hand side
ldrh r7, [r6] @ same for the right hand side, r6 now points to the right hand side location