diff options
Diffstat (limited to 'src/math/pow.c')
| -rw-r--r-- | src/math/pow.c | 65 |
1 files changed, 29 insertions, 36 deletions
diff --git a/src/math/pow.c b/src/math/pow.c index 052825a6..f257814e 100644 --- a/src/math/pow.c +++ b/src/math/pow.c @@ -21,24 +21,28 @@ * * Special cases: * 1. (anything) ** 0 is 1 - * 2. (anything) ** 1 is itself - * 3. (anything except 1) ** NAN is NAN, 1 ** NAN is 1 + * 2. 1 ** (anything) is 1 + * 3. (anything except 1) ** NAN is NAN * 4. NAN ** (anything except 0) is NAN * 5. +-(|x| > 1) ** +INF is +INF * 6. +-(|x| > 1) ** -INF is +0 * 7. +-(|x| < 1) ** +INF is +0 * 8. +-(|x| < 1) ** -INF is +INF - * 9. +-1 ** +-INF is 1 + * 9. -1 ** +-INF is 1 * 10. +0 ** (+anything except 0, NAN) is +0 * 11. -0 ** (+anything except 0, NAN, odd integer) is +0 - * 12. +0 ** (-anything except 0, NAN) is +INF - * 13. -0 ** (-anything except 0, NAN, odd integer) is +INF - * 14. -0 ** (odd integer) = -( +0 ** (odd integer) ) - * 15. +INF ** (+anything except 0,NAN) is +INF - * 16. +INF ** (-anything except 0,NAN) is +0 - * 17. -INF ** (anything) = -0 ** (-anything) - * 18. (-anything) ** (integer) is (-1)**(integer)*(+anything**integer) - * 19. (-anything except 0 and inf) ** (non-integer) is NAN + * 12. +0 ** (-anything except 0, NAN) is +INF, raise divbyzero + * 13. -0 ** (-anything except 0, NAN, odd integer) is +INF, raise divbyzero + * 14. -0 ** (+odd integer) is -0 + * 15. -0 ** (-odd integer) is -INF, raise divbyzero + * 16. +INF ** (+anything except 0,NAN) is +INF + * 17. +INF ** (-anything except 0,NAN) is +0 + * 18. -INF ** (+odd integer) is -INF + * 19. -INF ** (anything) = -0 ** (-anything), (anything except odd integer) + * 20. (anything) ** 1 is (anything) + * 21. (anything) ** -1 is 1/(anything) + * 22. (-anything) ** (integer) is (-1)**(integer)*(+anything**integer) + * 23. (-anything except 0 and inf) ** (non-integer) is NAN * * Accuracy: * pow(x,y) returns x**y nearly rounded. In particular @@ -98,18 +102,16 @@ double pow(double x, double y) ix = hx & 0x7fffffff; iy = hy & 0x7fffffff; - /* y == 0.0: x**0 = 1 */ + /* x**0 = 1, even if x is NaN */ if ((iy|ly) == 0) return 1.0; - - /* x == 1: 1**y = 1, even if y is NaN */ + /* 1**y = 1, even if y is NaN */ if (hx == 0x3ff00000 && lx == 0) return 1.0; - - /* y != 0.0: result is NaN if either arg is NaN */ + /* NaN if either arg is NaN */ if (ix > 0x7ff00000 || (ix == 0x7ff00000 && lx != 0) || iy > 0x7ff00000 || (iy == 0x7ff00000 && ly != 0)) - return (x+0.0) + (y+0.0); + return x + y; /* determine if y is an odd int when x < 0 * yisint = 0 ... y is not an integer @@ -142,13 +144,10 @@ double pow(double x, double y) else if (ix >= 0x3ff00000) /* (|x|>1)**+-inf = inf,0 */ return hy >= 0 ? y : 0.0; else /* (|x|<1)**+-inf = 0,inf */ - return hy < 0 ? -y : 0.0; - } - if (iy == 0x3ff00000) { /* y is +-1 */ - if (hy < 0) - return 1.0/x; - return x; + return hy >= 0 ? 0.0 : -y; } + if (iy == 0x3ff00000) /* y is +-1 */ + return hy >= 0 ? x : 1.0/x; if (hy == 0x40000000) /* y is 2 */ return x*x; if (hy == 0x3fe00000) { /* y is 0.5 */ @@ -174,19 +173,13 @@ double pow(double x, double y) } } - /* CYGNUS LOCAL + fdlibm-5.3 fix: This used to be - n = (hx>>31)+1; - but ANSI C says a right shift of a signed negative quantity is - implementation defined. */ - n = ((uint32_t)hx>>31) - 1; - - /* (x<0)**(non-int) is NaN */ - if ((n|yisint) == 0) - return (x-x)/(x-x); - - s = 1.0; /* s (sign of result -ve**odd) = -1 else = 1 */ - if ((n|(yisint-1)) == 0) - s = -1.0;/* (-ve)**(odd int) */ + s = 1.0; /* sign of result */ + if (hx < 0) { + if (yisint == 0) /* (x<0)**(non-int) is NaN */ + return (x-x)/(x-x); + if (yisint == 1) /* (x<0)**(odd int) */ + s = -1.0; + } /* |y| is huge */ if (iy > 0x41e00000) { /* if |y| > 2**31 */ |