peasant: update the random code

old random generator not very random.  The new one is, makes
the cliff climb impossibly hard

games/peasant/Makefile

@@ -133,7 +133,7 @@ qload_hd.o:	qload_hd.s qboot.inc \
 		hgr_copy.s \
 		gr_offsets.s \
 		qkumba_popwr.s \
-		random16.s
+		random8.s
 	ca65 -o qload_hd.o qload.s -DFLOPPY=0 -l qload_hd.lst
 
 ####
@@ -166,7 +166,7 @@ qload.o:	qload.s qboot.inc \
 		hgr_copy.s \
 		gr_offsets.s \
 		qkumba_popwr.s \
-		random16.s
+		random8.s
 	ca65 -o qload.o qload.s -DFLOPPY=1 -l qload.lst
 
 ###
@@ -248,7 +248,7 @@ qload.inc:	generate_common QLOAD
 	./generate_common -a 0xb00 -s location_names_l qload.lst >> qload.inc
 	./generate_common -a 0xb00 -s location_names_h qload.lst >> qload.inc
 	./generate_common -a 0xb00 -s wait_until_keypress qload.lst >> qload.inc
-	./generate_common -a 0xb00 -s random16 qload.lst >> qload.inc
+	./generate_common -a 0xb00 -s random8 qload.lst >> qload.inc
 	./generate_common -a 0xb00 -s score_points qload.lst >> qload.inc
 	./generate_common -a 0xb00 -s print_score qload.lst >> qload.inc
 	./generate_common -a 0xb00 -s update_score qload.lst >> qload.inc

games/peasant/climb/climb.s

@@ -227,7 +227,7 @@ skip_rock:
 	bne	move_bird
 maybe_new_bird:
 
-	jsr	random16
+	jsr	random8
 bird_freq_smc:
 	and	#$1f		; 1/32 of time start new bird?
 	bne	move_bird_done
@@ -235,7 +235,7 @@ bird_freq_smc:
 	; bird on base level,	12 .. 76	(MAP_LOCATION==0)
 	; bird on other levels, 12 .. 140
 
-	jsr	random16
+	jsr	random8
 
 	ldx	MAP_LOCATION
 	bne	new_bird_wider
@@ -313,7 +313,7 @@ move_rock_waiting:
 
 	; see if start new rock
 
-	jsr	random16
+	jsr	random8
 rock_freq_smc:
 	and	#$1f		; 1/32 of time start new rock
 	bne	rock_good
@@ -324,7 +324,7 @@ start_new_rock:
 	;	bit of a hack, really should be from 0..38
 	;	but we actually do 2..34 as it's easier
 
-	jsr	random16
+	jsr	random8
 	and	#$1f		; 0... 31
 	clc
 	adc	#2		; push away from edge a bit

games/peasant/kerrek_actions.s

@@ -194,7 +194,7 @@ kerrek_setup:
 	bne	kerrek_setup_dead
 
 kerrek_setup_alive:
-	jsr	random16
+	jsr	random8
 	and	#$1
 	beq	kerrek_alive_not_there
 kerrek_alive_out:

games/peasant/peasant1_actions.s

@@ -342,7 +342,7 @@ gary_scare_horse_mask:
 
 gary_scare_horse_nomask:
 
-	jsr	random16
+	jsr	random8
 	and	#$3		; 0..4
 	beq	gary_scare_try2
 	cmp	#$1

games/peasant/peasant3_actions.s

@@ -405,7 +405,7 @@ jhonka_cant_knock_door:
 	jmp	parse_common_unknown
 
 jhonka_knock_door:
-	jsr	random16
+	jsr	random8
 	and	#$7
 
 	beq	jhonka_knock5

games/peasant/peasant4.s

@@ -201,8 +201,9 @@ not_kerrek:
 	; init ned
 	;	randomly waits 126-64 frames
 
-	jsr	random16
+	jsr	random8
 	and	#$3f
+
 ;	lda	#64
 	sta	NED_STATUS
 

games/peasant/qload.s

@@ -100,7 +100,7 @@ load_file:
 .include "gr_offsets.s"
 .include "loadsave_menu.s"
 .include "wait_keypress.s"
-.include "random16.s"
+.include "random8.s"
 .include "score.s"
 ;.include "speaker_beeps.s"
 .include "redbook_sound.s"

games/peasant/random8.s

@@ -0,0 +1,24 @@
+; https://wimcouwenberg.wordpress.com/2020/11/15/a-fast-24-bit-prng-algorithm-for-the-6502-processor/
+
+random8:
+	lda	rand_a		; Operation 7 (with carry clear).
+	asl
+	eor	rand_b
+	sta	rand_b
+	rol			; Operation 9.
+	eor	rand_c
+	sta	rand_c
+	eor	rand_a		; Operation 5.
+	sta	rand_a
+	lda	rand_b		; Operation 15.
+	ror
+	eor	rand_c
+	sta	rand_c
+	eor	rand_b		; Operation 6.
+	sta	rand_b
+
+	rts
+
+rand_a:	.byte 0
+rand_b:	.byte 0
+rand_c:	.byte 1

random/Makefile

@@ -2,7 +2,15 @@ CC = gcc
 CFLAGS = -O2 -Wall
 LFLAGS =
 
-all:	random16 random8 #random15
+all:	random16 random8 random24
+
+###
+
+random24:	random24.o
+	$(CC) $(LFLAGS) -o random24 random24.o
+
+random24.o:	random24.c
+	$(CC) $(CFLAGS) -c random24.c
 
 ###
 
@@ -23,4 +31,4 @@ random8.o:	random8.c
 ###
 
 clean:
-	rm -f *~ *.o random16 random8 random15
+	rm -f *~ *.o random16 random8 random24

random/random24.c

@@ -0,0 +1,62 @@
+// https://wimcouwenberg.wordpress.com/2020/11/15/a-fast-24-bit-prng-algorithm-for-the-6502-processor/
+
+// lda a           ; Operation 7 (with carry clear).
+// asl
+// eor b
+// sta b
+// rol             ; Operation 9.
+// eor c
+// sta c
+// eor a           ; Operation 5.
+// sta a
+// lda b           ; Operation 15.
+// ror
+// eor c
+// sta c
+// eor b           ; Operation 6.
+// sta b
+
+
+#include <stdio.h>
+
+unsigned char a=0,b=0,c=1,carry,carry_new,accum;
+
+int rand24(void) {
+	accum=a;			// LDA A
+	carry=!!(accum&0x80);
+	accum<<=1;			// ASL
+	accum=accum^b;			// EOR B
+	b=accum;			// STA B
+	carry_new=!!(accum&0x80);	// ROL
+	accum<<=1;
+	accum|=carry;
+	carry=carry_new;
+	accum=accum^c;			// EOR C
+	c=accum;			// STA C
+	accum=accum^a;			// EOR A
+	a=accum;			// STA A
+	accum=b;			// LDA B
+	carry_new=accum&1;		// ROR
+	accum>>=1;
+	accum|=(carry<<7);
+	carry=carry_new;
+	accum=accum^c;			// EOR C
+	c=accum;			// STA C
+	accum=accum^b;			// EOR B
+	b=accum;			// STA B
+
+	return (a<<16)|(b<<8)|c;
+
+}
+
+int main(int argc, char **argv) {
+
+	int i,r;
+
+	for(i=0;i<1024;i++) {
+		r=rand24();
+		printf("%d: %06X m%02X\n",i,r,r&0x1f);
+	}
+
+	return 0;
+}