compat/drand48.c

   1 /*
   2  * Copyright (C) 1996-2015 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 #include "squid.h"
  10
  11 /* borrowed from libc/misc/drand48.c in Linux libc-5.4.46 this quick
  12  * hack by Martin Hamilton <martinh@gnu.org> to make Squid build on
  13  * Win32 with GNU-Win32 - sorry, folks! */
  14
  15 #if !HAVE_DRAND48
  16
  17 #define N   16
  18 #define MASK    ((unsigned)(1 << (N - 1)) + (1 << (N - 1)) - 1)
  19 #define LOW(x)  ((unsigned)(x) & MASK)
  20 #define HIGH(x) LOW((x) >> N)
  21 #define MUL(x, y, z)    { long l = (long)(x) * (long)(y); \
  22         (z)[0] = LOW(l); (z)[1] = HIGH(l); }
  23 #define CARRY(x, y) ((long)(x) + (long)(y) > MASK)
  24 #define ADDEQU(x, y, z) (z = CARRY(x, (y)), x = LOW(x + (y)))
  25 #define X0  0x330E
  26 #define X1  0xABCD
  27 #define X2  0x1234
  28 #define A0  0xE66D
  29 #define A1  0xDEEC
  30 #define A2  0x5
  31 #define C   0xB
  32
  33 static void next(void);
  34 static unsigned x[3] = {X0, X1, X2}, a[3] = {A0, A1, A2}, c = C;
  35
  36 double drand48(void);
  37
  38 double
  39 drand48(void)
  40 {
  41     static double two16m = 1.0 / (1L << N);
  42     next();
  43     return (two16m * (two16m * (two16m * x[0] + x[1]) + x[2]));
  44 }
  45
  46 static void
  47 next(void)
  48 {
  49     unsigned p[2], q[2], r[2], carry0, carry1;
  50
  51     MUL(a[0], x[0], p);
  52     ADDEQU(p[0], c, carry0);
  53     ADDEQU(p[1], carry0, carry1);
  54     MUL(a[0], x[1], q);
  55     ADDEQU(p[1], q[0], carry0);
  56     MUL(a[1], x[0], r);
  57     x[2] = LOW(carry0 + carry1 + CARRY(p[1], r[0]) + q[1] + r[1] +
  58                a[0] * x[2] + a[1] * x[1] + a[2] * x[0]);
  59     x[1] = LOW(p[1] + r[0]);
  60     x[0] = LOW(p[0]);
  61 }
  62
  63 #endif /* HAVE_DRAND48 */
  64