71 lines
1.7 KiB
ArmAsm
71 lines
1.7 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 - compare FAC1 with RAM location
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;
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; Input:
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; - .A - address low byte
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; - .Y - address high byte
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;
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; Output:
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; - .A - $00 for equal, $01 for FAC1 > RAM, $FF for FAC1 < RAM
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; - flags N/Z, Z=1 if equal, N=1 if FAC1 < RAM, Z=0, N=0 if FAC1 > RAM
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;
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; This is verified to be identical to the original Microsoft implementation where it was named FCOMP.
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;
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; Notes:
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; - uses vector at $24, leaves FAC1 and FAC2 unchanged (Codebase64)
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;
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; Alternative entry point: FCOMPN - Instead of A set INDEX2 to low byte of address
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;
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; See also:
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; - [CM64] Computes Mapping the Commodore 64 - page 115
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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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FCOMP:
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sta INDEX2+0
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FCOMPN:
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sty INDEX2+1
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ldy #0
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lda (INDEX2),Y
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iny
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tax
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beq sgn_FAC1_A ; arg is zero so sign of FAC1 will decide
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lda (INDEX2),Y
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eor FAC1_sign
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bmi sgn_FAC1_A_nozero ; signs differ so sign of FAC will decide
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cpx FAC1_exponent
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bne @1
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lda (INDEX2),Y
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ora #$80
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cmp FAC1_mantissa+0
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bne @1
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iny
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lda (INDEX2),Y
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cmp FAC1_mantissa+1
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bne @1
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iny
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lda (INDEX2),Y
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cmp FAC1_mantissa+2
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bne @1
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iny
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lda #$7F
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cmp FACOV
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lda (INDEX2),Y
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sbc FAC1_mantissa+3 ; Get zero if equal
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beq QINT_ret
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@1:
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lda FAC1_sign
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bcc @2
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eor #$FF
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@2:
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jmp sgn_A
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