e_acos.c 3.2 KB

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  1. /*
  2. * ====================================================
  3. * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  4. *
  5. * Developed at SunPro, a Sun Microsystems, Inc. business.
  6. * Permission to use, copy, modify, and distribute this
  7. * software is freely granted, provided that this notice
  8. * is preserved.
  9. * ====================================================
  10. */
  11. /* __ieee754_acos(x)
  12. * Method :
  13. * acos(x) = pi/2 - asin(x)
  14. * acos(-x) = pi/2 + asin(x)
  15. * For |x|<=0.5
  16. * acos(x) = pi/2 - (x + x*x^2*R(x^2)) (see asin.c)
  17. * For x>0.5
  18. * acos(x) = pi/2 - (pi/2 - 2asin(sqrt((1-x)/2)))
  19. * = 2asin(sqrt((1-x)/2))
  20. * = 2s + 2s*z*R(z) ...z=(1-x)/2, s=sqrt(z)
  21. * = 2f + (2c + 2s*z*R(z))
  22. * where f=hi part of s, and c = (z-f*f)/(s+f) is the correction term
  23. * for f so that f+c ~ sqrt(z).
  24. * For x<-0.5
  25. * acos(x) = pi - 2asin(sqrt((1-|x|)/2))
  26. * = pi - 0.5*(s+s*z*R(z)), where z=(1-|x|)/2,s=sqrt(z)
  27. *
  28. * Special cases:
  29. * if x is NaN, return x itself;
  30. * if |x|>1, return NaN with invalid signal.
  31. *
  32. * Function needed: __ieee754_sqrt
  33. */
  34. #include "math.h"
  35. #include "math_private.h"
  36. static const double
  37. one= 1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
  38. pi = 3.14159265358979311600e+00, /* 0x400921FB, 0x54442D18 */
  39. pio2_hi = 1.57079632679489655800e+00, /* 0x3FF921FB, 0x54442D18 */
  40. pio2_lo = 6.12323399573676603587e-17, /* 0x3C91A626, 0x33145C07 */
  41. pS0 = 1.66666666666666657415e-01, /* 0x3FC55555, 0x55555555 */
  42. pS1 = -3.25565818622400915405e-01, /* 0xBFD4D612, 0x03EB6F7D */
  43. pS2 = 2.01212532134862925881e-01, /* 0x3FC9C155, 0x0E884455 */
  44. pS3 = -4.00555345006794114027e-02, /* 0xBFA48228, 0xB5688F3B */
  45. pS4 = 7.91534994289814532176e-04, /* 0x3F49EFE0, 0x7501B288 */
  46. pS5 = 3.47933107596021167570e-05, /* 0x3F023DE1, 0x0DFDF709 */
  47. qS1 = -2.40339491173441421878e+00, /* 0xC0033A27, 0x1C8A2D4B */
  48. qS2 = 2.02094576023350569471e+00, /* 0x40002AE5, 0x9C598AC8 */
  49. qS3 = -6.88283971605453293030e-01, /* 0xBFE6066C, 0x1B8D0159 */
  50. qS4 = 7.70381505559019352791e-02; /* 0x3FB3B8C5, 0xB12E9282 */
  51. double attribute_hidden __ieee754_acos(double x)
  52. {
  53. double z,p,q,r,w,s,c,df;
  54. int32_t hx,ix;
  55. GET_HIGH_WORD(hx,x);
  56. ix = hx&0x7fffffff;
  57. if(ix>=0x3ff00000) { /* |x| >= 1 */
  58. u_int32_t lx;
  59. GET_LOW_WORD(lx,x);
  60. if(((ix-0x3ff00000)|lx)==0) { /* |x|==1 */
  61. if(hx>0) return 0.0; /* acos(1) = 0 */
  62. else return pi+2.0*pio2_lo; /* acos(-1)= pi */
  63. }
  64. return (x-x)/(x-x); /* acos(|x|>1) is NaN */
  65. }
  66. if(ix<0x3fe00000) { /* |x| < 0.5 */
  67. if(ix<=0x3c600000) return pio2_hi+pio2_lo;/*if|x|<2**-57*/
  68. z = x*x;
  69. p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  70. q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  71. r = p/q;
  72. return pio2_hi - (x - (pio2_lo-x*r));
  73. } else if (hx<0) { /* x < -0.5 */
  74. z = (one+x)*0.5;
  75. p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  76. q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  77. s = __ieee754_sqrt(z);
  78. r = p/q;
  79. w = r*s-pio2_lo;
  80. return pi - 2.0*(s+w);
  81. } else { /* x > 0.5 */
  82. z = (one-x)*0.5;
  83. s = __ieee754_sqrt(z);
  84. df = s;
  85. SET_LOW_WORD(df,0);
  86. c = (z-df*df)/(s+df);
  87. p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  88. q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  89. r = p/q;
  90. w = r*s+c;
  91. return 2.0*(df+w);
  92. }
  93. }