Browse code
Added a second PRNG with longer period
Andrew Alderwick authored on 25/08/2021 20:59:30
Showing 1 changed files
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@@ -1,7 +1,6 @@ |
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-( pseudo-random number generator ) |
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- |
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-( based on 16-bit xorshift algorithm discussed on |
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- http://www.retroprogramming.com/2017/07/xorshift-pseudorandom-numbers-in-z80.html ) |
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+( pseudo-random number generator, |
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+ based on two 16-bit xorshift algorithms by George Marsaglia |
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+ http://www.jstatsoft.org/v08/i14/paper ) |
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( devices ) |
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@@ -18,17 +17,22 @@ |
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|0100 ( -> ) |
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( init ) |
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;on-frame .Screen/vector DEO2 |
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+ |
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( seed prng (must be nonzero) ) |
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- .DateTime/month DEI .DateTime/day DEI |
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- #00 .DateTime/second #a0 SFT2 EOR2 |
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- #00 .DateTime/minute #40 SFT2 EOR2 |
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- .DateTime/hour EOR |
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+ #00 .DateTime/second DEI |
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+ #00 .DateTime/minute DEI #60 SFT2 EOR2 |
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+ #00 .DateTime/hour DEI #c0 SFT2 EOR2 ;prng2/x STA2 |
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+ #00 .DateTime/hour DEI #04 SFT2 |
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+ #00 .DateTime/day DEI #10 SFT2 EOR2 |
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+ #00 .DateTime/month DEI #60 SFT2 EOR2 |
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+ #00 .DateTime/year DEI #a0 SFT2 EOR2 ;prng2/y STA2 |
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+ ;prng2/x LDA2 ;prng2/y LDA2 EOR2 |
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ORAk ,&non-zero JCN INC2 &non-zero |
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;prng/seed STA2 |
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( theme ) |
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- #0fe5 .System/r DEO2 |
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- #0fc5 .System/g DEO2 |
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+ #0fe5 .System/r DEO2 |
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+ #0fc5 .System/g DEO2 |
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#0f25 .System/b DEO2 |
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BRK |
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@@ -42,16 +46,17 @@ |
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BRK |
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@draw-pixel |
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- ,prng JSR |
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+ ,prng2 JSR |
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#00 SWP .Screen/x DEO2 |
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#00 SWP .Screen/y DEO2 |
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#01 .Screen/pixel DEO |
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JMP2r |
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@prng ( -- number* ) |
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- ( returns the next number in the 65,535-long sequence, |
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+ ( returns the next number in a 65,535-long sequence, |
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which is never zero but every other 16-bit number |
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appears once before the sequence repeats ) |
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+ ( http://www.retroprogramming.com/2017/07/ xorshift-pseudorandom-numbers-in-z80.html ) |
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,&seed LDR2 |
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DUP2 #70 SFT2 EOR2 |
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DUP2 #09 SFT2 EOR2 |
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@@ -61,3 +66,17 @@ |
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&seed $2 |
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+@prng2 ( -- number* ) |
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+ ( returns the next number in a (2^32-1)-long sequence ) |
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+ ( http://b2d-f9r.blogspot.com/2010/08/ 16-bit-xorshift-rng-now-with-more.html ) |
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+ ,&x LDR2 |
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+ DUP2 #50 SFT2 EOR2 |
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+ DUP2 #03 SFT2 EOR2 |
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+ ,&y LDR2 DUP2 ,&x STR2 |
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+ DUP2 #01 SFT2 EOR2 EOR2 |
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+ ,&y STR2k POP |
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+ JMP2r |
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+ |
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+ &x $2 |
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+ &y $2 |
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+ |