Changeset 19520ba9 in mainline for uspace/lib/math/generic/log.c

Timestamp:

2021-06-18T16:05:49Z (3 years ago)

Author:

Maurizio Lombardi <mlombard@…>

Children:

f250c5a

Parents:

ec6081c

git-author:

Maurizio Lombardi <mlombard@…> (2018-11-25 16:43:14)

git-committer:

Maurizio Lombardi <mlombard@…> (2021-06-18 16:05:49)

Message:

math: sync log() to FreeBSD 11.2

File:

• uspace/lib/math/generic/log.c (modified) (2 diffs)

uspace/lib/math/generic/log.c

@@ -69 +69 @@
 #include <math.h>
 #include <stdint.h>
+
+#include "internal.h"
+
 static const double
-ln2_hi = 6.93147180369123816490e-01,  /* 3fe62e42 fee00000 */
-ln2_lo = 1.90821492927058770002e-10,  /* 3dea39ef 35793c76 */
+ln2_hi  =  6.93147180369123816490e-01,  /* 3fe62e42 fee00000 */
+ln2_lo  =  1.90821492927058770002e-10,  /* 3dea39ef 35793c76 */
+two54   =  1.80143985094819840000e+16,  /* 43500000 00000000 */
 Lg1 = 6.666666666666735130e-01,  /* 3FE55555 55555593 */
 Lg2 = 3.999999999940941908e-01,  /* 3FD99999 9997FA04 */
@@ -80 +84 @@
 Lg7 = 1.479819860511658591e-01;  /* 3FC2F112 DF3E5244 */
 
+static const double zero   =  0.0;
+static volatile double vzero = 0.0;
+
+
 double log(double x)
 {
-        union {double f; uint64_t i;} u = {x};
-        double_t hfsq,f,s,z,R,w,t1,t2,dk;
-        uint32_t hx;
-        int k;
-        hx = u.i>>32;
-        k = 0;
-        if (hx < 0x00100000 || hx>>31) {
-                if (u.i<<1 == 0)
-                        return -1/(x*x);  /* log(+-0)=-inf */
-                if (hx>>31)
-                        return (x-x)/0.0; /* log(-#) = NaN */
-                /* subnormal number, scale x up */
-                k -= 54;
-                x *= 0x1p54;
-                u.f = x;
-                hx = u.i>>32;
-        } else if (hx >= 0x7ff00000) {
-                return x;
-        } else if (hx == 0x3ff00000 && u.i<<32 == 0)
-                return 0;
+        double hfsq,f,s,z,R,w,t1,t2,dk;
+        int32_t k,hx,i,j;
+        uint32_t lx;
 
-        /* reduce x into [sqrt(2)/2, sqrt(2)] */
-        hx += 0x3ff00000 - 0x3fe6a09e;
-        k += (int)(hx>>20) - 0x3ff;
-        hx = (hx&0x000fffff) + 0x3fe6a09e;
-        u.i = (uint64_t)hx<<32 | (u.i&0xffffffff);
-        x = u.f;
-        f = x - 1.0;
-        hfsq = 0.5*f*f;
-        s = f/(2.0+f);
+        EXTRACT_WORDS(hx,lx,x);
+
+        k=0;
+        if (hx < 0x00100000) {                  /* x < 2**-1022  */
+            if (((hx&0x7fffffff)|lx)==0) 
+                return -two54/vzero;            /* log(+-0)=-inf */
+            if (hx<0) return (x-x)/zero;        /* log(-#) = NaN */
+            k -= 54; x *= two54; /* subnormal number, scale up x */
+            GET_HIGH_WORD(hx,x);
+        } 
+        if (hx >= 0x7ff00000) return x+x;
+        k += (hx>>20)-1023;
+        hx &= 0x000fffff;
+        i = (hx+0x95f64)&0x100000;
+        SET_HIGH_WORD(x,hx|(i^0x3ff00000));     /* normalize x or x/2 */
+        k += (i>>20);
+        f = x-1.0;
+        if((0x000fffff&(2+hx))<3) {     /* -2**-20 <= f < 2**-20 */
+            if(f==zero) {
+                if(k==0) {
+                    return zero;
+                } else {
+                    dk=(double)k;
+                    return dk*ln2_hi+dk*ln2_lo;
+                }
+            }
+            R = f*f*(0.5-0.33333333333333333*f);
+            if(k==0) return f-R; else {dk=(double)k;
+                     return dk*ln2_hi-((R-dk*ln2_lo)-f);}
+        }
+        s = f/(2.0+f); 
+        dk = (double)k;
         z = s*s;
+        i = hx-0x6147a;
         w = z*z;
-        t1 = w*(Lg2+w*(Lg4+w*Lg6));
-        t2 = z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
-        R = t2 + t1;
-        dk = k;
-
-        return s*(hfsq+R) + dk*ln2_lo - hfsq + f + dk*ln2_hi;
+        j = 0x6b851-hx;
+        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=0.5*f*f;
+            if(k==0) return f-(hfsq-s*(hfsq+R)); else
+                     return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
+        } else {
+            if(k==0) return f-s*(f-R); else
+                     return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
+        }
 }