s_cos.c 2.1 KB

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  1. /* @(#)s_cos.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_cos.c,v 1.7 1995/05/10 20:47:02 jtc Exp $";
  14. #endif
  15. /* cos(x)
  16. * Return cosine function of x.
  17. *
  18. * kernel function:
  19. * __kernel_sin ... sine function on [-pi/4,pi/4]
  20. * __kernel_cos ... cosine function on [-pi/4,pi/4]
  21. * __ieee754_rem_pio2 ... argument reduction routine
  22. *
  23. * Method.
  24. * Let S,C and T denote the sin, cos and tan respectively on
  25. * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
  26. * in [-pi/4 , +pi/4], and let n = k mod 4.
  27. * We have
  28. *
  29. * n sin(x) cos(x) tan(x)
  30. * ----------------------------------------------------------
  31. * 0 S C T
  32. * 1 C -S -1/T
  33. * 2 -S -C T
  34. * 3 -C S -1/T
  35. * ----------------------------------------------------------
  36. *
  37. * Special cases:
  38. * Let trig be any of sin, cos, or tan.
  39. * trig(+-INF) is NaN, with signals;
  40. * trig(NaN) is that NaN;
  41. *
  42. * Accuracy:
  43. * TRIG(x) returns trig(x) nearly rounded
  44. */
  45. #include "math.h"
  46. #include "math_private.h"
  47. #ifdef __STDC__
  48. double cos(double x)
  49. #else
  50. double cos(x)
  51. double x;
  52. #endif
  53. {
  54. double y[2],z=0.0;
  55. int32_t n, ix;
  56. /* High word of x. */
  57. GET_HIGH_WORD(ix,x);
  58. /* |x| ~< pi/4 */
  59. ix &= 0x7fffffff;
  60. if(ix <= 0x3fe921fb) return __kernel_cos(x,z);
  61. /* cos(Inf or NaN) is NaN */
  62. else if (ix>=0x7ff00000) return x-x;
  63. /* argument reduction needed */
  64. else {
  65. n = __ieee754_rem_pio2(x,y);
  66. switch(n&3) {
  67. case 0: return __kernel_cos(y[0],y[1]);
  68. case 1: return -__kernel_sin(y[0],y[1],1);
  69. case 2: return -__kernel_cos(y[0],y[1]);
  70. default:
  71. return __kernel_sin(y[0],y[1],1);
  72. }
  73. }
  74. }
  75. libm_hidden_def(cos)