Differences

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--- base:16bit_xorshift_random_generator [2019-05-10 02:09] – vsariola
+++ base:16bit_xorshift_random_generator [2019-05-10 02:45] – vsariola
@@ Line 20: / Line 20: @@
 </code>
-Here is an implementation for the C64. 25 cycles without the RTS.
+Here is an implementation for the C64. 30 cycles without the RTS.
 <code asm>
@@ Line 32: / Line 32: @@
         ...
         ; the RNG, you can get 8-bit random numbers in A, leaves X/Y unchanged
-random  LDA rng_zp_low
+random  LDA rng_zp_high
         LSR
+        LDA rng_zp_low
+        ROR
         EOR rng_zp_high
         STA rng_zp_high ; high part of x ^= x << 7 done
-        ROR             ; A has now x >> 9 and the high bit of the low byte
+        ROR             ; A has now x >> 9 and high bit comes from low byte
         EOR rng_zp_low
-        STA rng_zp_low  ; x ^= x >> 9 done
+        STA rng_zp_low  ; x ^= x >> 9 and the low part of x ^= x << 7 done
         EOR rng_zp_high
         STA rng_zp_high ; x ^= x << 8 done