IEEE float log2 implementation.
authordrepper <drepper>
Wed, 6 Jun 2001 12:50:56 +0000 (12:50 +0000)
committerdrepper <drepper>
Wed, 6 Jun 2001 12:50:56 +0000 (12:50 +0000)
sysdeps/ieee754/flt-32/e_log2f.c [new file with mode: 0644]

diff --git a/sysdeps/ieee754/flt-32/e_log2f.c b/sysdeps/ieee754/flt-32/e_log2f.c
new file mode 100644 (file)
index 0000000..af3c6ea
--- /dev/null
@@ -0,0 +1,90 @@
+/* e_logf.c -- float version of e_log.c.
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
+ * adapted for log2 by Ulrich Drepper <drepper@cygnus.com>
+ */
+
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+
+#include "math.h"
+#include "math_private.h"
+
+#ifdef __STDC__
+static const float
+#else
+static float
+#endif
+ln2 = 0.69314718055994530942,
+two25 =    3.355443200e+07,    /* 0x4c000000 */
+Lg1 = 6.6666668653e-01,        /* 3F2AAAAB */
+Lg2 = 4.0000000596e-01,        /* 3ECCCCCD */
+Lg3 = 2.8571429849e-01, /* 3E924925 */
+Lg4 = 2.2222198546e-01, /* 3E638E29 */
+Lg5 = 1.8183572590e-01, /* 3E3A3325 */
+Lg6 = 1.5313838422e-01, /* 3E1CD04F */
+Lg7 = 1.4798198640e-01; /* 3E178897 */
+
+#ifdef __STDC__
+static const float zero   =  0.0;
+#else
+static float zero   =  0.0;
+#endif
+
+#ifdef __STDC__
+       float __ieee754_log2f(float x)
+#else
+       float __ieee754_log2f(x)
+       float x;
+#endif
+{
+       float hfsq,f,s,z,R,w,t1,t2,dk;
+       int32_t k,ix,i,j;
+
+       GET_FLOAT_WORD(ix,x);
+
+       k=0;
+       if (ix < 0x00800000) {                  /* x < 2**-126  */
+           if ((ix&0x7fffffff)==0)
+               return -two25/(x-x);            /* log(+-0)=-inf */
+           if (ix<0) return (x-x)/(x-x);       /* log(-#) = NaN */
+           k -= 25; x *= two25; /* subnormal number, scale up x */
+           GET_FLOAT_WORD(ix,x);
+       }
+       if (ix >= 0x7f800000) return x+x;
+       k += (ix>>23)-127;
+       ix &= 0x007fffff;
+       i = (ix+(0x95f64<<3))&0x800000;
+       SET_FLOAT_WORD(x,ix|(i^0x3f800000));    /* normalize x or x/2 */
+       k += (i>>23);
+       dk = (float)k;
+       f = x-(float)1.0;
+       if((0x007fffff&(15+ix))<16) {   /* |f| < 2**-20 */
+           if(f==zero) return dk;
+           R = f*f*((float)0.5-(float)0.33333333333333333*f);
+           return dk-(R-f)/ln2;
+       }
+       s = f/((float)2.0+f);
+       z = s*s;
+       i = ix-(0x6147a<<3);
+       w = z*z;
+       j = (0x6b851<<3)-ix;
+       t1= w*(Lg2+w*(Lg4+w*Lg6));
+       t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
+       i |= j;
+       R = t2+t1;
+       if(i>0) {
+           hfsq=(float)0.5*f*f;
+           return dk-((hfsq-(s*(hfsq+R)))-f)/ln2;
+       } else {
+           return dk-((s*(f-R))-f)/ln2;
+       }
+}