178 lines
3.9 KiB
C
178 lines
3.9 KiB
C
/*
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* drand48, etc. pseudo-random number generator
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* This implementation assumes unsigned short integers of at least
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* 16 bits, long integers of at least 32 bits, and ignores
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* overflows on adding or multiplying two unsigned integers.
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* Two's-complement representation is assumed in a few places.
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* Some extra masking is done if unsigneds are exactly 16 bits
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* or longs are exactly 32 bits, but so what?
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* An assembly-language implementation would run significantly faster.
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*/
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#ifndef HAVEFP
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#define HAVEFP 1
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#endif
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#define N 16
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#define MASK ((unsigned)(1 << (N - 1)) + (1 << (N - 1)) - 1)
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#define LOW(x) ((unsigned)(x) & MASK)
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#define HIGH(x) LOW((x) >> N)
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#define MUL(x, y, z) { long l = (long)(x) * (long)(y); \
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(z)[0] = LOW(l); (z)[1] = HIGH(l); }
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#define CARRY(x, y) ((long)(x) + (long)(y) > MASK)
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#define ADDEQU(x, y, z) (z = CARRY(x, (y)), x = LOW(x + (y)))
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#define X0 0x330E
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#define X1 0xABCD
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#define X2 0x1234
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#define A0 0xE66D
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#define A1 0xDEEC
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#define A2 0x5
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#define C 0xB
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#define SET3(x, x0, x1, x2) ((x)[0] = (x0), (x)[1] = (x1), (x)[2] = (x2))
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#define SETLOW(x, y, n) SET3(x, LOW((y)[n]), LOW((y)[(n)+1]), LOW((y)[(n)+2]))
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#define SEED(x0, x1, x2) (SET3(x, x0, x1, x2), SET3(a, A0, A1, A2), c = C)
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#define REST(v) for (i = 0; i < 3; i++) { xsubi[i] = x[i]; x[i] = temp[i]; } \
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return (v);
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#define NEST(TYPE, f, F) TYPE f(xsubi) register unsigned short *xsubi; { \
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register int i; register TYPE v; unsigned temp[3]; \
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for (i = 0; i < 3; i++) { temp[i] = x[i]; x[i] = LOW(xsubi[i]); } \
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v = F(); REST(v); }
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#define HI_BIT (1L << (2 * N - 1))
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static unsigned x[3] = { X0, X1, X2 }, a[3] = { A0, A1, A2 }, c = C;
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static unsigned short lastx[3];
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static void next();
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#if HAVEFP
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double
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drand48()
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{
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static double two16m = 1.0 / (1L << N);
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next();
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return (two16m * (two16m * (two16m * x[0] + x[1]) + x[2]));
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}
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NEST(double, erand48, drand48);
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#else
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long
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irand48(m)
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/* Treat x[i] as a 48-bit fraction, and multiply it by the 16-bit
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* multiplier m. Return integer part as result.
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*/
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register unsigned short m;
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{
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unsigned r[4], p[2], carry0 = 0;
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next();
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MUL(m, x[0], &r[0]);
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MUL(m, x[2], &r[2]);
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MUL(m, x[1], p);
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if (CARRY(r[1], p[0]))
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ADDEQU(r[2], 1, carry0);
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return (r[3] + carry0 + CARRY(r[2], p[1]));
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}
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long
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krand48(xsubi, m)
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/* same as irand48, except user provides storage in xsubi[] */
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register unsigned short *xsubi;
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unsigned short m;
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{
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register int i;
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register long iv;
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unsigned temp[3];
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for (i = 0; i < 3; i++) {
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temp[i] = x[i];
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x[i] = xsubi[i];
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}
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iv = irand48(m);
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REST(iv);
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}
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#endif
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long
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lrand48()
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{
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next();
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return (((long)x[2] << (N - 1)) + (x[1] >> 1));
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}
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long
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mrand48()
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{
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register long l;
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next();
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/* sign-extend in case length of a long > 32 bits
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(as on Honeywell) */
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return ((l = ((long)x[2] << N) + x[1]) & HI_BIT ? l | -HI_BIT : l);
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}
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static void
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next()
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{
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unsigned p[2], q[2], r[2], carry0, carry1;
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MUL(a[0], x[0], p);
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ADDEQU(p[0], c, carry0);
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ADDEQU(p[1], carry0, carry1);
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MUL(a[0], x[1], q);
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ADDEQU(p[1], q[0], carry0);
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MUL(a[1], x[0], r);
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x[2] = LOW(carry0 + carry1 + CARRY(p[1], r[0]) + q[1] + r[1] +
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a[0] * x[2] + a[1] * x[1] + a[2] * x[0]);
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x[1] = LOW(p[1] + r[0]);
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x[0] = LOW(p[0]);
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}
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void
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srand48(seedval)
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long seedval;
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{
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SEED(X0, LOW(seedval), HIGH(seedval));
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}
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unsigned short *
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seed48(seed16v)
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unsigned short seed16v[3];
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{
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SETLOW(lastx, x, 0);
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SEED(LOW(seed16v[0]), LOW(seed16v[1]), LOW(seed16v[2]));
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return (lastx);
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}
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void
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lcong48(param)
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unsigned short param[7];
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{
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SETLOW(x, param, 0);
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SETLOW(a, param, 3);
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c = LOW(param[6]);
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}
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NEST(long, nrand48, lrand48);
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NEST(long, jrand48, mrand48);
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#ifdef DRIVER
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/*
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This should print the sequences of integers in Tables 2
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and 1 of the TM:
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1623, 3442, 1447, 1829, 1305, ...
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657EB7255101, D72A0C966378, 5A743C062A23, ...
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*/
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#include <stdio.h>
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main()
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{
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int i;
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for (i = 0; i < 80; i++) {
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printf("%4d ", (int)(4096 * drand48()));
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printf("%.4X%.4X%.4X\n", x[2], x[1], x[0]);
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}
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}
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#endif
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