85 lines
1.9 KiB
ArmAsm
85 lines
1.9 KiB
ArmAsm
;; #LAYOUT# STD * #TAKE
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;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
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;; #LAYOUT# * BASIC_0 #TAKE
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;; #LAYOUT# * * #IGNORE
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; This file is under the MIT license, it contains code released by Microsoft Corporation.
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; See LICENSE for more information.
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; Math package - add FAC2 to FAC1
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;
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; Input:
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; - .A - must load FAC1 exponent ($61) beforehand to set the zero flag
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;
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; This is verified to be identical to the original Microsoft implementation where it was named FADDT.
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;
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;
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; See also:
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; - [CM64] Computes Mapping the Commodore 64 - page 112
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; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
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; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
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;
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add_FAC2_FAC1:
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bne @1 ; If FAC1=0 result is in FAC2
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jmp mov_FAC2_FAC1
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@1:
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ldx FACOV
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stx OLDOV
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ldx #FAC2_exponent
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lda FAC2_exponent
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FADDC:
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tay
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beq ZERRTS
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sec
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sbc FAC1_exponent
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beq FADD4 ; No shifting
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bcc @1 ; Branch if FAC2_exponent < FAC1_exponent
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sty FAC1_exponent ; Resulting exponent
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ldy FAC2_sign ; Since FAC2 is larger, its
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sty FAC1_sign ; sign is sign of result
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eor #$FF ; Shift a negative number of places
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adc #0 ; Complete negation C=1
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ldy #0
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sty OLDOV
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ldx #FAC1_exponent
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bne @2
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@1:
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ldy #0
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sty FACOV
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@2:
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cmp #$F9
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bmi add_align_exponents
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tay
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lda FACOV
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lsr 1,X
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jsr short_shift_FAC
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FADD4:
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bit ARISGN
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bpl add_mantissas_FAC2_FAC1
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ldy #FAC1_exponent
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cpx #FAC2_exponent ; FAC1 is bigger
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beq @1
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ldy #FAC2_exponent ; FAC2 is bigger
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@1:
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sec
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eor #$FF
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adc OLDOV
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sta FACOV
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lda 4,Y
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sbc 4,X
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sta FAC1_mantissa+3
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lda 3,Y
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sbc 3,X
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sta FAC1_mantissa+2
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lda 2,Y
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sbc 2,X
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sta FAC1_mantissa+1
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lda 1,Y
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sbc 1,X
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sta FAC1_mantissa+0
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; Fallthrough to abs_and_normalize_FAC1
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