Save 16 bytes in the CGB boot ROM

BootROMs/cgb_boot.asm

@@ -181,8 +181,7 @@ ENDC
     dec c
     jr nz, .expandPalettesLoop
 
-    ld hl, BgPalettes
-    call LoadBGPalettes64
+    call LoadPalettesFromHRAM
 
     ; Turn on LCD
     ld a, $91
@@ -530,7 +529,7 @@ Palettes:
     dw $7FFF, $7FEA, $7D5F, $0000 ; CGA 1
     dw $4778, $3290, $1D87, $0861 ; DMG LCD
 
-KeyCombinationPalettes
+KeyCombinationPalettes:
     db 1  * 3  ; Right
     db 48 * 3  ; Left
     db 5  * 3  ; Up
@@ -795,7 +794,6 @@ IF !DEF(FAST)
 .fadeLoop
     ld c, 32 ; 32 colors to fade
     ld hl, BgPalettes
-    push hl
 .frameLoop
     push bc
 
@@ -848,8 +846,7 @@ IF !DEF(FAST)
     jr nz, .frameLoop
 
     call WaitFrame
-    pop hl
-    call LoadBGPalettes64
+    call LoadPalettesFromHRAM
     call WaitFrame
     dec b
     jr nz, .fadeLoop
@@ -907,7 +904,7 @@ ENDC
 
 GetKeyComboPalette:
     ld hl, KeyCombinationPalettes - 1 ; Return value is 1-based, 0 means nothing down
-    ld c ,a
+    ld c, a
     ld b, 0
     add hl, bc
     ld a, [hl]
@@ -1006,6 +1003,7 @@ GetPaletteIndex:
     xor a
     ret
 
+; optimizations in callers rely on this returning with b = 0
 GetPaletteCombo:
     ld hl, PaletteCombinations
     ld b, 0
@@ -1022,7 +1020,7 @@ LoadPalettesFromIndex: ; a = index of combination
     ld a, [hli]
     push hl
     ld hl, Palettes
-    ld b, 0
+    ; b is already 0
     ld c, a
     add hl, bc
     ld d, 8
@@ -1035,15 +1033,15 @@ LoadPalettesFromIndex: ; a = index of combination
     jr .loadObjPalette
 .loadBGPalette
     ;BG Palette
-    ld a, [hli]
+    ld c, [hl]
+    ; b is already 0
     ld hl, Palettes
-    ld b, 0
-    ld c, a
     add hl, bc
     ld d, 8
     jr LoadBGPalettes
 
-LoadBGPalettes64:
+LoadPalettesFromHRAM:
+    ld hl, BgPalettes
     ld d, 64
 
 LoadBGPalettes:
@@ -1076,6 +1074,7 @@ _ClearVRAMViaHDMA:
     jr nz, .loop
     ret
 
+; clobbers AF and HL
 GetInputPaletteIndex:
     ld a, $20 ; Select directions
     ldh [$00], a
@@ -1083,11 +1082,10 @@ GetInputPaletteIndex:
     cpl
     and $F
     ret z ; No direction keys pressed, no palette
-    push bc
-    ld c, 0
 
+    ld l, 0
 .directionLoop
-    inc c
+    inc l
     rra
     jr nc, .directionLoop
 
@@ -1100,15 +1098,13 @@ GetInputPaletteIndex:
     rla
     rla
     and $C
-    add c
-    ld b, a
+    add l
+    ld l, a
     ldh a, [InputPalette]
-    ld c, a
-    ld a, b
-    ldh [InputPalette], a
-    cp c
-    pop bc
+    cp l
     ret z ; No change, don't load
+    ld a, l
+    ldh [InputPalette], a
     ; Slide into change Animation Palette
 
 ChangeAnimationPalette:
@@ -1118,10 +1114,8 @@ ChangeAnimationPalette:
     call GetPaletteCombo
     inc l
     inc l
-    ld a, [hl]
+    ld c, [hl]
     ld hl, Palettes + 1
-    ld b, 0
-    ld c, a
     add hl, bc
     ld a, [hld]
     cp $7F ; Is white color?
@@ -1186,8 +1180,7 @@ ChangeAnimationPalette:
 
 
     call WaitFrame
-    ld hl, BgPalettes
-    call LoadBGPalettes64
+    call LoadPalettesFromHRAM
     ; Delay the wait loop while the user is selecting a palette
     ld a, 45
     ldh [WaitLoopCounter], a