Free 2 bytes again.

[cc65] / libsrc / runtime / mul.s

diff --git a/libsrc/runtime/mul.s b/libsrc/runtime/mul.s
index 769cf9d8e9274c7c2e9f50063dfe7f707a7f4af0..087e639fc57ccc15470e7581dad6915e60204f32 100644 (file)
--- a/libsrc/runtime/mul.s
+++ b/libsrc/runtime/mul.s
@@ -19,12 +19,12 @@ tosumulax:
         txa                     ; High byte zero
         beq     @L3             ; Do 8x16 multiplication if high byte zero
         stx     ptr4+1          ; Save right operand
-        jsr     popptr1         ; Get left operand (Y=0 by popptr1)
+        jsr     popptr1         ; Get left operand (Y=0, X untouched by popptr1)
 
 ; Do ptr4:ptr4+1 * ptr1:ptr1+1 --> AX
 
-        tya                    ; A = 0        
-        ldx     ptr1+1          ; check if lhs is 8 bit only
+        tya                     ; A = 0        
+        ldy     ptr1+1          ; check if lhs is 8 bit only
         beq     @L4             ; -> we can do 8x16 after swap
         sta     tmp1
         ldy     #16             ; Number of bits
@@ -36,7 +36,7 @@ tosumulax:
         clc
         adc     ptr1
         tax
-        lda     ptr1+1          ; hi byte of left op         
+        lda     ptr1+1          ; Hi byte of left op         
         adc     tmp1
         sta     tmp1
         txa
@@ -56,15 +56,15 @@ tosumulax:
 
 @L3:    jmp     mul8x16
 
-; If the high byte of rhs is zero, swap the operands and use the 8x16
-; routine. On entry, A and X are zero
+; If the high byte of lhs is zero, swap the operands in ptr1/4 and
+; use the 8x16 routine. On entry, A and Y are zero and X has the value
+; of ptr4+1
 
-@L4:    ldy     ptr1            ; Save right operand (8 bit)
+@L4:    stx     ptr1+1          ; Store hi-byte from ptr4
+        ldy     ptr1            ; Save right operand (8 bit)
         ldx     ptr4            ; Copy left 16 bit operand to right
         stx     ptr1
-        ldx     ptr4+1          ; swap high-byte too
-        stx     ptr1+1
         sty     ptr4            ; Copy low 8 bit of right op to left
         ldy     #8
-        jmp     mul8x16a
+        jmp     mul8x16a        ; There, ptr4+1 will be also cleared