98 lines
1.9 KiB
ArmAsm
98 lines
1.9 KiB
ArmAsm
;; Multiply Floating Point Accumulator by 10
|
|
;; = 8x + 2x
|
|
;; Implement by shifting MAC left one bit,
|
|
;; and then keeping that value to add on after
|
|
;; shifting two more bits left.
|
|
;; This should be done using basic_fac1_overflow to
|
|
;; hold the overflow bits, so that the result can
|
|
;; be exponent adjusted after, if required.
|
|
|
|
fac1_mul10:
|
|
lda #$00
|
|
sta basic_fac1_overflow
|
|
|
|
;; Multiply mantissa by 2
|
|
jsr fac1_mantissa_mul2
|
|
|
|
;; copy down to BASIC numeric work area at $57
|
|
;; (basic_numeric_work_area)
|
|
;; (We copy all 7 bytes off the FAC1, so that we have
|
|
;; the overflow bits, and the copy is as small as possible)
|
|
ldx #7
|
|
f1m10_l1:
|
|
lda basic_fac1_mantissa,x
|
|
sta basic_numeric_work_area,x
|
|
dex
|
|
bpl f1m10_l1
|
|
|
|
;; Multiply mantissa by 4, so it is now 8x original
|
|
jsr fac1_mantissa_mul2
|
|
jsr fac1_mantissa_mul2
|
|
|
|
;; Now add stored value of 2x to it, to get the total x10
|
|
ldy #3
|
|
ldx #0
|
|
clc
|
|
f1m10_l2:
|
|
lda basic_fac1_mantissa,x
|
|
adc basic_numeric_work_area,x
|
|
sta basic_fac1_mantissa,x
|
|
inx
|
|
dey
|
|
bpl f1m10_l2
|
|
lda basic_fac1_overflow
|
|
adc basic_numeric_work_area+7
|
|
sta basic_fac1_overflow
|
|
|
|
;; Now shift right and increase exponent until overflow
|
|
;; bits = $00
|
|
f1m10_l3:
|
|
lda basic_fac1_overflow
|
|
bne +
|
|
;; All done, return
|
|
clc
|
|
rts
|
|
*
|
|
;; Divide mantissa by two, and increment exponent
|
|
jsr fac1_mantissa_div2
|
|
inc basic_fac1_exponent
|
|
lda basic_fac1_exponent
|
|
bpl f1m10_l3
|
|
;; Exponent has bit 7 set, so has wrapped.
|
|
;; = OVERFLOW ERROR
|
|
jmp do_OVERFLOW_error
|
|
|
|
fac1_mantissa_mul2:
|
|
ldy #3
|
|
ldx #0
|
|
clc
|
|
f1m1_l1:
|
|
;; Multiply mantissa by 2, and store overflow
|
|
;; in basic_fac1_bits
|
|
lda basic_fac1_mantissa,x
|
|
rol
|
|
sta basic_fac1_mantissa,x
|
|
inx
|
|
dey
|
|
bpl f1m1_l1
|
|
lda basic_fac1_overflow
|
|
rol
|
|
sta basic_fac1_overflow
|
|
|
|
rts
|
|
|
|
fac1_mantissa_div2:
|
|
;; Divide mantissa by 2, including using overflow bits
|
|
clc
|
|
lda basic_fac1_overflow
|
|
ror
|
|
sta basic_fac1_overflow
|
|
ldy #3
|
|
f1md2_l1:
|
|
lda basic_fac1_mantissa,y
|
|
ror
|
|
sta basic_fac1_mantissa,y
|
|
dey
|
|
bpl f1md2_l1
|
|
rts
|