From: Brad Smith <rainwarrior@gmail.com>
Date: Tue, 12 Jul 2016 00:48:47 +0000 (-0400)
Subject: Fix broken rand() implementation. The high 8 bits were unused, reducing it to a 24... 
X-Git-Tag: V2.16~89^2
X-Git-Url: https://git.sur5r.net/?a=commitdiff_plain;h=refs%2Fpull%2F323%2Fhead;p=cc65

Fix broken rand() implementation. The high 8 bits were unused, reducing it to a 24-bit implementation (while still doing all the work for a 32-bit one). The best entropy is in the unused high byte, returning these bits in A instead of bits 8-15, which had considerably lower entropy (i.e. rand() & 255 was effectively a 16-bit LCG).
---

diff --git a/libsrc/common/rand.s b/libsrc/common/rand.s
index 48a88b7c4..8ad7bcdb4 100644
--- a/libsrc/common/rand.s
+++ b/libsrc/common/rand.s
@@ -44,7 +44,6 @@ _rand:  clc
         lda     rand+1
         adc     #$59
         sta     rand+1
-        pha
         lda     rand+2
         adc     #$41
         sta     rand+2
@@ -53,8 +52,7 @@ _rand:  clc
         lda     rand+3
         adc     #$31
         sta     rand+3
-        pla                     ; return bit 8-22 in (X,A)
-        rts
+        rts                     ; return bit (16-22,24-31) in (X,A)
 
 _srand: sta     rand+0          ; Store the seed
         stx     rand+1