6502/cc65
1
0
Fork 0
mirror of https://github.com/cc65/cc65.git synced 2024-12-23 04:30:10 +00:00
Code Issues Projects Releases Wiki Activity

Free 2 bytes again.

Browse Source
This commit is contained in:
IrgendwerA8 2018-05-29 01:47:04 +02:00
parent 0f108cb4d8
commit 465a651090
1 changed files with 10 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
libsrc/runtime/mul.s
View File

@ -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
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