From f4779208e34d4205ca8f15e503689be3e68464d6 Mon Sep 17 00:00:00 2001
From: Gwilym Inzani <email@gwilym.dev>
Date: Tue, 27 Jun 2023 21:48:01 +0100
Subject: [PATCH] Implement first cases for the non stereo

---
 agb/src/sound/mixer/mixer.s     | 29 +++++++++++++++++++++--------
 agb/src/sound/mixer/sw_mixer.rs | 10 +++++++++-
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/agb/src/sound/mixer/mixer.s b/agb/src/sound/mixer/mixer.s
index 5806373c..254699c6 100644
--- a/agb/src/sound/mixer/mixer.s
+++ b/agb/src/sound/mixer/mixer.s
@@ -4,7 +4,8 @@
 agb_rs__buffer_size:
     .word 0
 
-agb_arm_func agb_rs__mixer_add
+.macro mixer_add fn_name:req is_first:req
+agb_arm_func \fn_name
     @ Arguments
     @ r0 - pointer to the data to be copied (u8 array)
     @ r1 - pointer to the sound buffer (i16 array which will alternate left and right channels, 32-bit aligned)
@@ -18,9 +19,9 @@ agb_arm_func agb_rs__mixer_add
     ldr r7, [sp, #20]        @ load the right channel modification amount into r7
 
     cmp r7, r3               @ check if left and right channel need the same modifications
-    beq .Lsame_modification
+    beq 3f @ same modification
 
-.Lmodifications_fallback:
+4:  @ modification fallback
     orr r7, r7, r3, lsl #16   @ r7 now is the left channel followed by the right channel modifications.
 
     mov r5, #0                   @ current index we're reading from
@@ -34,9 +35,12 @@ agb_arm_func agb_rs__mixer_add
     ldrsb r6, [r4]           @ load the current sound sample to r6
     add r5, r5, r2           @ calculate the position to read the next sample from
 
+.ifc is_first,true
+    mul r4, r6, r7           @ r4 = r6 * r7 (calculating both the left and right samples together)
+.else
     ldr r4, [r1]             @ read the current value
-
     mla r4, r6, r7, r4       @ r4 += r6 * r7 (calculating both the left and right samples together)
+.endif
 
     str r4, [r1], #4         @ store the new value, and increment the pointer
 .endr
@@ -47,13 +51,13 @@ agb_arm_func agb_rs__mixer_add
     pop {{r4-r8}}
     bx lr
 
-.Lsame_modification:
+3: @ same modification
     @ check to see if this is a perfect power of 2
     @ r5 is a scratch register, r7 = r3 = amount to modify
     sub r5, r7, #1
     ands r5, r5, r7
 
-    bne .Lmodifications_fallback @ not 0 means we need to do the full modification
+    bne 4b @ not 0 means we need to do the full modification, jump to modification fallback
 
     @ count leading zeros of r7 into r3
     mov r3, #0
@@ -74,11 +78,16 @@ agb_arm_func agb_rs__mixer_add
     ldrsb r6, [r4]            @ load the current sound sample to r6
     add r5, r5, r2           @ calculate the position to read the next sample from
 
-    ldr r4, [r1]             @ read the current value
 
     lsl r6, r6, #16
     orr r6, r6, lsr #16
+
+.ifc is_first,true
+    mov r4, r6, lsl r3       @ r4 = r6 << r3
+.else
+    ldr r4, [r1]             @ read the current value
     add r4, r4, r6, lsl r3   @ r4 += r6 << r3 (calculating both the left and right samples together)
+.endif
 
     str r4, [r1], #4         @ store the new value, and increment the pointer
 .endr
@@ -89,7 +98,11 @@ agb_arm_func agb_rs__mixer_add
     pop {{r4-r8}}
     bx lr
 
-agb_arm_end agb_rs__mixer_add
+agb_arm_end \fn_name
+.endm
+
+mixer_add agb_rs__mixer_add false
+mixer_add agb_rs__mixer_add_first true
 
 .macro stereo_add_fn fn_name:req is_first:req
 agb_arm_func \fn_name
diff --git a/agb/src/sound/mixer/sw_mixer.rs b/agb/src/sound/mixer/sw_mixer.rs
index efa4ce23..ffa637f3 100644
--- a/agb/src/sound/mixer/sw_mixer.rs
+++ b/agb/src/sound/mixer/sw_mixer.rs
@@ -29,6 +29,14 @@ extern "C" {
         right_amount: Num<i16, 4>,
     );
 
+    fn agb_rs__mixer_add_first(
+        sound_data: *const u8,
+        sound_buffer: *mut Num<i16, 4>,
+        playback_speed: Num<u32, 8>,
+        left_amount: Num<i16, 4>,
+        right_amount: Num<i16, 4>,
+    );
+
     fn agb_rs__mixer_add_stereo(
         sound_data: *const u8,
         sound_buffer: *mut Num<i16, 4>,
@@ -412,7 +420,7 @@ impl MixerBuffer {
         working_buffer: &mut [Num<i16, 4>],
         channels: impl Iterator<Item = &'a mut SoundChannel>,
     ) {
-        // working_buffer.fill(0.into());
+        working_buffer.fill(0.into());
 
         for channel in channels {
             if channel.is_done {