Rikard Nordgren
5a3f65efa4
Also change to only use bit 7 as sign in FAC1 and FAC2 (as the original BASIC does) to simplify implementations.
50 lines
920 B
ArmAsm
50 lines
920 B
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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;
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; Math package - Mov MEM to FAC2 with address in INDEX zero page register
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;
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; See also:
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; - https://sourceforge.net/p/acme-crossass/code-0/38/tree/trunk/ACME_Lib/cbm/c64/float.a?force=True
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;
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; XXX implement, test
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get_FAC2_via_INDEX:
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; Now copy the data from RAM to FAC2, for the format description see:
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; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic#Representation_in_the_C-64
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; Copy the mantissa
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ldy #$04
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lda (INDEX), y
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sta FAC2_mantissa+3
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dey
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lda (INDEX), y
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sta FAC2_mantissa+2
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dey
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lda (INDEX), y
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sta FAC2_mantissa+1
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dey
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lda (INDEX), y
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sta FAC2_sign
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ora #$80 ; clear the sign bit
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sta FAC2_mantissa+0
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; Copy the exponent
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dey
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lda (INDEX), y
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sta FAC2_exponent
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; Return the FAC1 exponent
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lda FAC1_exponent
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rts
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