s_logb.c 1.0 KB

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  1. /* @(#)s_logb.c 5.1 93/09/24 */
  2. /*
  3. * ====================================================
  4. * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  5. *
  6. * Developed at SunPro, a Sun Microsystems, Inc. business.
  7. * Permission to use, copy, modify, and distribute this
  8. * software is freely granted, provided that this notice
  9. * is preserved.
  10. * ====================================================
  11. */
  12. #if defined(LIBM_SCCS) && !defined(lint)
  13. static char rcsid[] = "$NetBSD: s_logb.c,v 1.8 1995/05/10 20:47:50 jtc Exp $";
  14. #endif
  15. /*
  16. * double logb(x)
  17. * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
  18. * Use ilogb instead.
  19. */
  20. #include "math.h"
  21. #include "math_private.h"
  22. #ifdef __STDC__
  23. double logb(double x)
  24. #else
  25. double logb(x)
  26. double x;
  27. #endif
  28. {
  29. int32_t lx,ix;
  30. EXTRACT_WORDS(ix,lx,x);
  31. ix &= 0x7fffffff; /* high |x| */
  32. if((ix|lx)==0) return -1.0/fabs(x);
  33. if(ix>=0x7ff00000) return x*x;
  34. if((ix>>=20)==0) /* IEEE 754 logb */
  35. return -1022.0;
  36. else
  37. return (double) (ix-1023);
  38. }
  39. libm_hidden_def(logb)