Implement a pseudo random number generator for RND/RANDOMIZE

Author: tcort

Makefile.am

@@ -32,6 +32,7 @@ tcbasic_SOURCES = \
 	line.h		line.c \
 	mulop.h		mulop.c \
 	number.h	number.c \
+	prng.h		prng.c \
 	rem.h		rem.c \
 	relop.h		relop.c \
 	rnd.h		rnd.c \

configure.ac

@@ -26,7 +26,7 @@ AC_PROG_CC
 AC_HEADER_STDC
 
 AC_CHECK_HEADERS([getopt.h])
-AC_CHECK_FUNCS([arc4random arc4random_uniform getopt_long strsep])
+AC_CHECK_FUNCS([getopt_long strsep])
 
 AC_CONFIG_HEADERS([config.h:config.in])
 

prng.c

@@ -0,0 +1,32 @@
+/*
+    tcbasic - a small BASIC Interpreter written in C.
+    Copyright (C) 2015  Thomas Cort <linuxgeek@gmail.com>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+
+static unsigned long tcb_seed = 1;
+
+#define A 16807
+#define M 2147483647
+
+void tcb_srand(unsigned long seed) {
+	tcb_seed = (seed == 0) ? 1 : seed;
+}
+
+float tcb_rand(void) {
+	tcb_seed = (A * tcb_seed) % M;
+	return tcb_seed / (float) M;
+}

prng.h

@@ -0,0 +1,25 @@
+/*
+    tcbasic - a small BASIC Interpreter written in C.
+    Copyright (C) 2015  Thomas Cort <linuxgeek@gmail.com>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef __PRNG_H
+#define __PRNG_H
+
+void tcb_srand(unsigned long seed);
+float tcb_rand(void);
+
+#endif

rnd.c

@@ -21,6 +21,7 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "prng.h"
 #include "tokenizer.h"
 
 #include "number.h"
@@ -52,10 +53,7 @@ struct rnd *parse_rnd(struct tokenizer *t) {
 }
 
 struct number *eval_rnd(struct rnd *r) {
-
-	/* IEEE 754 floating point -- exponent is 2^-1, mantissa is "random" */
-        int x = 0x3f000000 | (rand() & 0x7FFFFF);
-	return new_number_from_float(*((float*)&x));
+	return new_number_from_float(tcb_rand());
 }
 
 void print_rnd(struct rnd *r) {

statement.c

@@ -23,6 +23,7 @@
 #include <time.h>
 
 #include "buffer.h"
+#include "prng.h"
 #include "readaline.h"
 #include "runtime.h"
 #include "tokenizer.h"
@@ -306,7 +307,7 @@ int eval_statement(struct statement *s, int number, int next_number) {
 		case REM:
 			break;
 		case RANDOMIZE:
-			srand(time(NULL));
+			tcb_srand(time(NULL));
 			break;
 	}