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authornsz <nsz@port70.net>2012-03-20 20:04:53 +0100
committernsz <nsz@port70.net>2012-03-20 20:04:53 +0100
commitf1347a3a453ce38bf55cd92f5922311235810fd1 (patch)
treef34ab3397f7b51e07c360f7a926ccbc6b452748a /src
parent615bbd365f322cd8d0b1a4383ee0a6ce8e35b33b (diff)
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clean up pow.c and powf.c
fix comments about special cases
Diffstat (limited to 'src')
-rw-r--r--src/math/pow.c65
-rw-r--r--src/math/powf.c35
2 files changed, 43 insertions, 57 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 */
diff --git a/src/math/powf.c b/src/math/powf.c
index c101d95c..427c8965 100644
--- a/src/math/powf.c
+++ b/src/math/powf.c
@@ -57,17 +57,15 @@ float powf(float x, float y)
ix = hx & 0x7fffffff;
iy = hy & 0x7fffffff;
- /* y == 0: x**0 = 1 */
+ /* x**0 = 1, even if x is NaN */
if (iy == 0)
return 1.0f;
-
- /* x == 1: 1**y = 1, even if y is NaN */
+ /* 1**y = 1, even if y is NaN */
if (hx == 0x3f800000)
return 1.0f;
-
- /* y != 0: result is NaN if either arg is NaN */
+ /* NaN if either arg is NaN */
if (ix > 0x7f800000 || iy > 0x7f800000)
- return (x+0.0f) + (y+0.0f);
+ return x + y;
/* determine if y is an odd int when x < 0
* yisint = 0 ... y is not an integer
@@ -93,13 +91,10 @@ float powf(float x, float y)
else if (ix > 0x3f800000) /* (|x|>1)**+-inf = inf,0 */
return hy >= 0 ? y : 0.0f;
else /* (|x|<1)**+-inf = 0,inf */
- return hy < 0 ? -y : 0.0f;
- }
- if (iy == 0x3f800000) { /* y is +-1 */
- if (hy < 0)
- return 1.0f/x;
- return x;
+ return hy >= 0 ? 0.0f: -y;
}
+ if (iy == 0x3f800000) /* y is +-1 */
+ return hy >= 0 ? x : 1.0f/x;
if (hy == 0x40000000) /* y is 2 */
return x*x;
if (hy == 0x3f000000) { /* y is 0.5 */
@@ -122,15 +117,13 @@ float powf(float x, float y)
return z;
}
- n = ((uint32_t)hx>>31) - 1;
-
- /* (x<0)**(non-int) is NaN */
- if ((n|yisint) == 0)
- return (x-x)/(x-x);
-
- sn = 1.0f; /* s (sign of result -ve**odd) = -1 else = 1 */
- if ((n|(yisint-1)) == 0) /* (-ve)**(odd int) */
- sn = -1.0f;
+ sn = 1.0f; /* 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) */
+ sn = -1.0f;
+ }
/* |y| is huge */
if (iy > 0x4d000000) { /* if |y| > 2**27 */