37 lines
1.2 KiB
ArmAsm
37 lines
1.2 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 - Convert signed 16-bit integer to floating point
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;
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; This is verified to be identical to the original Microsoft implementation where it was named FLOATS.
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;
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; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
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; - https://www.c64-wiki.com/wiki/GIVAYF (which calls this function)
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;
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; Convert the signed 16-bit integer in FAC1 mantissa ($62:$63)
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; into a floating point number in FAC1. Assume X=exponent
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;
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; Alternative entry points:
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; FLOATC: Assume FAC1_mantissa+0 and +1 loaded. Assume CF=0 if negative and C=1 if positive
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; FLOATB: as for FLOATC and do not clear FAC1_mantissa+2 and +3 and set sign and FACOV to A
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convert_i16_to_FAC1:
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lda FAC1_mantissa+0
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eor #$FF
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rol ; CF = Complement of sign
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FLOATC:
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lda #0
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sta FAC1_mantissa+3
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sta FAC1_mantissa+2
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FLOATB:
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stx FAC1_exponent
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sta FACOV
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sta FAC1_sign
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jmp abs_and_normal_FAC1
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