86 lines
1.9 KiB
ArmAsm
86 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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;
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; Math package - divide FAC2 (dividend) by FAC1 (divisor)
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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 (but our routine does not need this)
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;
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; Output:
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; - FAC1
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;
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; Note:
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; - some documentation suggest this is a division leaving quotient and remainder (left in FAC2),
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; but it seems (experimentation) that this is not true
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;
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; See also:
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; - [CM64] Computes Mapping the Commodore 64 - page 114
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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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div_FAC2_FAC1:
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; 'Pamiętaj, cholero - nie dziel przez zero!' - ancient polish proverb
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lda FAC1_exponent
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+beq do_DIVISION_BY_ZERO_error
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; Handle special case - dividing 0 by non-zero value
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lda FAC2_exponent
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+beq clear_FAC1
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; Multiply signs
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lda FAC1_sign
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eor FAC2_sign
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sta FAC1_sign
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; Subtract the exponents
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lda #$A0 ; correction for bias and FAC2 digits
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sta RESHO+0
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lda #$00
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sta RESHO+1
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lda FAC2_exponent ; add FAC2 exponent to temporary variable
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jsr muldiv_RESHO_01_add_A
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lda RESHO+0 ; subtract FAC1 exponent from temporary variable
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sec
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sbc FAC1_exponent
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sta RESHO+0
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bcs @1
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dec RESHO+1
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@1:
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lda RESHO+1
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+bmi clear_FAC1 ; result too low, set 0 and quit
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lda RESHO+0
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sta FAC1_exponent
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; Divide the mantissas
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jsr div_FAC1_denorm
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jsr muldiv_RESHO_set_0
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jsr div_mantissas
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; Copy the result to FAC1 - XXX we probably already have similar code somewhere...
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lda FAC2_mantissa+3
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sta FAC1_mantissa+3
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lda FAC2_mantissa+2
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sta FAC1_mantissa+2
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lda FAC2_mantissa+1
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sta FAC1_mantissa+1
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lda FAC2_mantissa+0
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sta FAC1_mantissa+0
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; Normalize and quit
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jmp normal_FAC1
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