drand48.c
上传用户:liugui
上传日期:2007-01-04
资源大小:822k
文件大小:1k
- /* borrowed from libc/misc/drand48.c in Linux libc-5.4.46 this quick
- hack by Martin Hamilton <martinh@gnu.org> to make Squid build on
- Win32 with GNU-Win32 - sorry, folks! */
- #ifndef HAVE_DRAND48
- #define N 16
- #define MASK ((unsigned)(1 << (N - 1)) + (1 << (N - 1)) - 1)
- #define LOW(x) ((unsigned)(x) & MASK)
- #define HIGH(x) LOW((x) >> N)
- #define MUL(x, y, z) { long l = (long)(x) * (long)(y);
- (z)[0] = LOW(l); (z)[1] = HIGH(l); }
- #define CARRY(x, y) ((long)(x) + (long)(y) > MASK)
- #define ADDEQU(x, y, z) (z = CARRY(x, (y)), x = LOW(x + (y)))
- #define X0 0x330E
- #define X1 0xABCD
- #define X2 0x1234
- #define A0 0xE66D
- #define A1 0xDEEC
- #define A2 0x5
- #define C 0xB
- static void next( void );
- static unsigned x[3] = { X0, X1, X2 }, a[3] = { A0, A1, A2 }, c = C;
- double drand48( void );
- double
- drand48( void )
- {
- static double two16m = 1.0 / (1L << N);
- next();
- return (two16m * (two16m * (two16m * x[0] + x[1]) + x[2]));
- }
- static void
- next( void )
- {
- unsigned p[2], q[2], r[2], carry0, carry1;
- MUL(a[0], x[0], p);
- ADDEQU(p[0], c, carry0);
- ADDEQU(p[1], carry0, carry1);
- MUL(a[0], x[1], q);
- ADDEQU(p[1], q[0], carry0);
- MUL(a[1], x[0], r);
- x[2] = LOW(carry0 + carry1 + CARRY(p[1], r[0]) + q[1] + r[1] +
- a[0] * x[2] + a[1] * x[1] + a[2] * x[0]);
- x[1] = LOW(p[1] + r[0]);
- x[0] = LOW(p[0]);
- }
- #endif /* HAVE_DRAND48 */