add JavaScript Interpreter

components/external/espruino/libs/math/drand.c

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+/*							drand.c
+ *
+ *	Pseudorandom number generator
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * double y, drand();
+ *
+ * drand( &y );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Yields a random number 1.0 <= y < 2.0.
+ *
+ * The three-generator congruential algorithm by Brian
+ * Wichmann and David Hill (BYTE magazine, March, 1987,
+ * pp 127-8) is used. The period, given by them, is
+ * 6953607871644.
+ *
+ * Versions invoked by the different arithmetic compile
+ * time options DEC, IBMPC, and MIEEE, produce
+ * approximately the same sequences, differing only in the
+ * least significant bits of the numbers. The UNK option
+ * implements the algorithm as recommended in the BYTE
+ * article.  It may be used on all computers. However,
+ * the low order bits of a double precision number may
+ * not be adequately random, and may vary due to arithmetic
+ * implementation details on different computers.
+ *
+ * The other compile options generate an additional random
+ * integer that overwrites the low order bits of the double
+ * precision number.  This reduces the period by a factor of
+ * two but tends to overcome the problems mentioned.
+ *
+ */
+
+
+/*  Three-generator random number algorithm
+ * of Brian Wichmann and David Hill
+ * BYTE magazine, March, 1987 pp 127-8
+ *
+ * The period, given by them, is (p-1)(q-1)(r-1)/4 = 6.95e12.
+ */
+
+#include "mconf.h"
+#ifdef ANSIPROT
+static int ranwh ( void );
+#else
+static int ranwh();
+#endif
+
+static int sx = 1;
+static int sy = 10000;
+static int sz = 3000;
+
+static union {
+ double d;
+ unsigned short s[4];
+} unkans;
+
+/* This function implements the three
+ * congruential generators.
+ */
+ 
+static int ranwh()
+{
+int r, s;
+
+/*  sx = sx * 171 mod 30269 */
+r = sx/177;
+s = sx - 177 * r;
+sx = 171 * s - 2 * r;
+if( sx < 0 )
+	sx += 30269;
+
+
+/* sy = sy * 172 mod 30307 */
+r = sy/176;
+s = sy - 176 * r;
+sy = 172 * s - 35 * r;
+if( sy < 0 )
+	sy += 30307;
+
+/* sz = 170 * sz mod 30323 */
+r = sz/178;
+s = sz - 178 * r;
+sz = 170 * s - 63 * r;
+if( sz < 0 )
+	sz += 30323;
+/* The results are in static sx, sy, sz. */
+return 0;
+}
+
+/*	drand.c
+ *
+ * Random double precision floating point number between 1 and 2.
+ *
+ * C callable:
+ *	drand( &x );
+ */
+
+int drand( a )
+double *a;
+{
+unsigned short r;
+#ifdef DEC
+unsigned short s, t;
+#endif
+
+/* This algorithm of Wichmann and Hill computes a floating point
+ * result:
+ */
+ranwh();
+unkans.d = sx/30269.0  +  sy/30307.0  +  sz/30323.0;
+r = unkans.d;
+unkans.d -= r;
+unkans.d += 1.0;
+
+/* if UNK option, do nothing further.
+ * Otherwise, make a random 16 bit integer
+ * to overwrite the least significant word
+ * of unkans.
+ */
+#ifdef UNK
+/* do nothing */
+#else
+ranwh();
+r = sx * sy + sz;
+#endif
+
+#ifdef DEC
+/* To make the numbers as similar as possible
+ * in all arithmetics, the random integer has
+ * to be inserted 3 bits higher up in a DEC number.
+ * An alternative would be put it 3 bits lower down
+ * in all the other number types.
+ */
+s = unkans.s[2];
+t = s & 07;	/* save these bits to put in at the bottom */
+s &= 0177770;
+s |= (r >> 13) & 07;
+unkans.s[2] = s;
+t |= r << 3;
+unkans.s[3] = t;
+#endif
+
+#ifdef IBMPC
+unkans.s[0] = r;
+#endif
+
+#ifdef MIEEE
+unkans.s[3] = r;
+#endif
+
+*a = unkans.d;
+return 0;
+}