mirror of https://github.com/jeremysrand/BuGS.git
139 lines
2.3 KiB
ArmAsm
139 lines
2.3 KiB
ArmAsm
;
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; random.s
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; BuGS
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;
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; Created by Jeremy Rand on 2020-07-19.
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;Copyright © 2020 Jeremy Rand. All rights reserved.
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;
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;
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; This code was suggested by John Brooks
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;
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; If you need a random range less than 16 bits, here the smaller EOR constants:
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; BITS EOR_CONST
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; 2 $0003
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; 3 $0006
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; 4 $000C
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; 5 $0014
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; 6 $0030
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; 7 $0060
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; 8 $00B8
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; 9 $0110
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; 10 $0240
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; 11 $0500
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; 12 $0CA0
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; 13 $1B00
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; 14 $3500
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; 15 $6000
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; 16 $B400
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;
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case on
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mcopy random.macros
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keep random
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random start
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randInit entry
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lda randomSeed
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sta seed65535
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and #$1f
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bne randInit_store32
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lda #$1f
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randInit_store32 anop
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sta seed32
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and #$f
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bne randInit_store16
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lda #$f
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randInit_store16 anop
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sta seed16
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rtl
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; Returns a number from 0 to 14
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rand0_to_14 entry
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lda seed16
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lsr a
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bcc skipEor16
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eor #$000c
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skipEor16 anop
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sta seed16
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dec a
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rtl
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; Returns a number from 0 to N-1 where N is <= 15, arrives in the accumulator
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randN entry
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cmp #2
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blt randN_ret0
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cmp #2
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beq randN_power2
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cmp #4
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beq randN_power2
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cmp #8
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beq randN_power2
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bra randN_doit
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randN_power2 anop
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dec a
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sta upperLimit
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jsl rand0_to_65534
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and upperLimit
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rtl
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randN_ret0 anop
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lda #0
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rtl
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randN_doit anop
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sta upperLimit
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jsl rand0_to_14
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randN_loop anop
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cmp upperLimit
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blt randN_done
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sec
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sbc upperLimit
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bra randN_loop
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randN_done anop
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rtl
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; Returns a number from 0 to 30
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rand0_to_30 entry
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lda seed32
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lsr a
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bcc skipEor32
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eor #$0014
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skipEor32 anop
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sta seed32
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dec a
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rtl
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; returns a number from 0 to 24
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rand25 entry
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jsl rand0_to_30
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cmp #25
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bge rand25
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rtl
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; Returns a number from 0 to 65534
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rand0_to_65534 entry
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lda seed65535
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lsr a
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bcc skipEor65535
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eor #$b400
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skipEor65535 anop
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sta seed65535
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dec a
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rtl
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seed65535 dc i2'0'
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seed32 dc i2'0'
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seed16 dc i2'0'
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upperLimit dc i2'0'
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end
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