From fdce67f8ba6b4aa310e35cd2123b4c72db122a81 Mon Sep 17 00:00:00 2001
From: Keith Stellyes <keithstellyes@Keiths-MacBook-Pro.local>
Date: Sun, 13 Oct 2019 12:44:43 -0700
Subject: [PATCH] Implement RNG in kernel and basic dice app to demonstrate it

---
 apps/dice/glue.asm          |  6 +++++
 apps/dice/main.asm          | 46 +++++++++++++++++++++++++++++++++++++
 kernel/random.asm           | 29 +++++++++++++++++++++++
 tools/emul/.gitignore       |  1 +
 tools/emul/Makefile         |  2 +-
 tools/emul/dice/user.h      |  2 ++
 tools/emul/shell/shell_.asm |  3 +++
 tools/emul/shell/user.h     |  2 ++
 8 files changed, 90 insertions(+), 1 deletion(-)
 create mode 100644 apps/dice/glue.asm
 create mode 100644 apps/dice/main.asm
 create mode 100644 kernel/random.asm
 create mode 100644 tools/emul/dice/user.h

diff --git a/apps/dice/glue.asm b/apps/dice/glue.asm
new file mode 100644
index 0000000..507f77c
--- /dev/null
+++ b/apps/dice/glue.asm
@@ -0,0 +1,6 @@
+.inc	"user.h"
+
+.org	USER_CODE
+	jp diceMain
+.equ	DICE_RAMSTART	USER_RAMSTART
+.inc	"dice/main.asm"
\ No newline at end of file
diff --git a/apps/dice/main.asm b/apps/dice/main.asm
new file mode 100644
index 0000000..1b91ee1
--- /dev/null
+++ b/apps/dice/main.asm
@@ -0,0 +1,46 @@
+; dice - A simple RNG application
+; Generates a random number in the range of 0000-FFFF
+; Perhaps would be handy to make more user-friendly in the-future 
+; (and to use entropy). Right now, more proof-of-concept of RNG functionality
+; than anything.
+
+.equ SEED DICE_RAMSTART
+
+diceMain:
+	ld	hl, sInputSeed
+	call	printstr
+	call	stdioReadLine
+	call	printcrlf
+	xor	a ; ensure C is not set
+	call	parseHexPair
+	jp	c, unknownSeedInput
+	ld	(SEED), a
+	call	parseHexPair
+	jp	c, unknownSeedInput
+	ld (SEED+1), a
+	ld hl, (SEED)
+.diceMainLoop:
+	call	stdioReadLine
+	ld	a, (hl)
+	cp	'q'
+	jp z, diceExit
+	ld	hl, (SEED)
+	call	rnd
+	ld	(SEED), hl
+	call	printHexPair
+	call	printcrlf
+	jp .diceMainLoop
+
+unknownSeedInput:
+	ld a, '?'
+	call	stdioPutC
+	call	printcrlf
+	jp diceMain
+
+diceExit:
+	call	printcrlf
+	xor a
+	ret
+
+sInputSeed:
+	.db	"Please input seed in hex (0000-FFFF):", 0
\ No newline at end of file
diff --git a/kernel/random.asm b/kernel/random.asm
new file mode 100644
index 0000000..de31182
--- /dev/null
+++ b/kernel/random.asm
@@ -0,0 +1,29 @@
+; Part of kernel because ideally we have some sort of entropy. For now,
+; just having it be user-provided for prototypical purposes.
+; Implementation by John Metcalf of 
+; http://www.retroprogramming.com/2017/07/xorshift-pseudorandom-numbers-in-z80.html
+; (Slightly altered for CollapseOS)
+;
+; 16-bit xorshift pseudorandom number generator
+; 
+; in: hl = seed
+; out: hl = pseudorandom number (generally fed into the next call)
+; corrupts   a
+
+rnd:
+  ld a,h
+  rra
+  ld a,l
+  rra
+  xor h
+  ld h,a
+  ld a,l
+  rra
+  ld a,h
+  rra
+  xor l
+  ld l,a
+  xor h
+  ld h,a
+
+  ret
\ No newline at end of file
diff --git a/tools/emul/.gitignore b/tools/emul/.gitignore
index cc529d7..4fe12a1 100644
--- a/tools/emul/.gitignore
+++ b/tools/emul/.gitignore
@@ -5,3 +5,4 @@
 /cfsin/zasm
 /cfsin/ed
 /cfsin/user.h
+/cfsin/dice
diff --git a/tools/emul/Makefile b/tools/emul/Makefile
index 69511f3..7a7fa56 100644
--- a/tools/emul/Makefile
+++ b/tools/emul/Makefile
@@ -4,7 +4,7 @@ KERNEL = ../../kernel
 APPS = ../../apps
 ZASMBIN = zasm/zasm
 ZASMSH = ../zasm.sh
-SHELLAPPS = $(addprefix cfsin/, zasm ed)
+SHELLAPPS = $(addprefix cfsin/, zasm ed dice)
 CFSIN_CONTENTS = $(SHELLAPPS) cfsin/user.h
 
 .PHONY: all
diff --git a/tools/emul/dice/user.h b/tools/emul/dice/user.h
new file mode 100644
index 0000000..5693a82
--- /dev/null
+++ b/tools/emul/dice/user.h
@@ -0,0 +1,2 @@
+.equ	USER_CODE 0x4200
+.equ	USER_RAMSTART 0x6000
\ No newline at end of file
diff --git a/tools/emul/shell/shell_.asm b/tools/emul/shell/shell_.asm
index efa54b0..9803141 100644
--- a/tools/emul/shell/shell_.asm
+++ b/tools/emul/shell/shell_.asm
@@ -39,10 +39,13 @@
 	jp	printcrlf
 	jp	stdioPutC
 	jp	stdioReadLine
+	jp	printHexPair
+	jp	rnd
 
 .inc "core.asm"
 .inc "err.h"
 .inc "parse.asm"
+.inc "random.asm"
 
 .equ	BLOCKDEV_RAMSTART	RAMSTART
 .equ	BLOCKDEV_COUNT		4
diff --git a/tools/emul/shell/user.h b/tools/emul/shell/user.h
index 8e19e6b..49e5c2c 100644
--- a/tools/emul/shell/user.h
+++ b/tools/emul/shell/user.h
@@ -32,3 +32,5 @@
 .equ	printcrlf		@+3
 .equ	stdioPutC		@+3
 .equ	stdioReadLine	@+3
+.equ	printHexPair	@+3
+.equ	rnd	@+3
\ No newline at end of file