From 3fea9aada05567178f0c7b7a33d1f5b157a9625e Mon Sep 17 00:00:00 2001
From: Gwilym Kuiper <gw@ilym.me>
Date: Wed, 4 May 2022 17:58:24 +0100
Subject: [PATCH] Somehow reduce clamp_s8 by 1 instruction

---
 agb/src/sound/mixer/mixer.s | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/agb/src/sound/mixer/mixer.s b/agb/src/sound/mixer/mixer.s
index ba4796b6..667607a1 100644
--- a/agb/src/sound/mixer/mixer.s
+++ b/agb/src/sound/mixer/mixer.s
@@ -155,19 +155,24 @@ 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, r5, r6}
+    push {r4, r5, r6, r7, r8, r9, r10}
+
+CONST_0   .req r7
+CONST_FF  .req r8
+CONST_127 .req r9
+TEMP      .req r10
+
+    ldr CONST_0, =0
+    ldr CONST_FF, =0xff
+    ldr CONST_127, =127
 
     ldr r2, agb_rs__buffer_size @ loop counter
     mov r4, r2
 
 .macro clamp_s8 reg:req
-    cmn \reg, #128
-    mvnlt \reg, #128
-
-    cmp \reg, #127
-    movgt \reg, #127
-
-    and \reg, \reg, #255
+    add \reg, \reg, #127
+    subs r10, r7, \reg, asr #8
+    andne \reg, r8, r10, lsr #24
 .endm
 
 .macro load_sample left_reg:req right_reg:req
@@ -197,12 +202,16 @@ agb_arm_func agb_rs__mixer_collapse
     orr r3, r3, r5, lsl #24
     orr r12, r12, r6, lsl #24
 
+    ldr r5, =0x80808080
+    eor r3, r3, r5
+    eor r12, r12, r5
+
     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, r5, r6}
+    pop {r4, r5, r6, r7, r8, r9, r10}
     bx lr
 agb_arm_end agb_rs__mixer_collapse