Changeset f250c5a in mainline for uspace/lib/math/generic/scalbn.c

Timestamp:

2021-06-18T16:05:56Z (3 years ago)

Author:

Maurizio Lombardi <mlombard@…>

Children:

197d59d

Parents:

19520ba9

git-author:

Maurizio Lombardi <mlombard@…> (2018-11-25 16:43:33)

git-committer:

Maurizio Lombardi <mlombard@…> (2021-06-18 16:05:56)

Message:

math: sync scalbn to FreeBSD 11.2

File:

• uspace/lib/math/generic/scalbn.c (modified) (1 diff)

uspace/lib/math/generic/scalbn.c

@@ -18 +18 @@
 #include <stdint.h>
 
+#include "internal.h"
 
-/* scalbn(x,n) returns x* 2**n  computed by  exponent
+/*
+ * scalbn (double x, int n)
+ * scalbn(x,n) returns x* 2**n  computed by  exponent
  * manipulation rather than by actually performing an
  * exponentiation or a multiplication.
  */
 
-double scalbn(double x, int n)
+static const double
+two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
+twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
+huge   = 1.0e+300,
+tiny   = 1.0e-300;
+
+double
+scalbn (double x, int n)
 {
-        union {double f; uint64_t i;} u;
-        double_t y = x;
-
-        if (n > 1023) {
-                y *= 0x1p1023;
-                n -= 1023;
-                if (n > 1023) {
-                        y *= 0x1p1023;
-                        n -= 1023;
-                        if (n > 1023)
-                                n = 1023;
-                }
-        } else if (n < -1022) {
-        /* make sure final n < -53 to avoid double
-           rounding in the subnormal range */
-                y *= 0x1p-1022 * 0x1p53;
-                n += 1022 - 53;
-                if (n < -1022) {
-                        y *= 0x1p-1022 * 0x1p53;
-                        n += 1022 - 53;
-                        if (n < -1022)
-                                n = -1022;
-                }
+        int32_t k,hx,lx;
+        EXTRACT_WORDS(hx,lx,x);
+        k = (hx&0x7ff00000)>>20;                /* extract exponent */
+        if (k==0) {                             /* 0 or subnormal x */
+            if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
+            x *= two54;
+            GET_HIGH_WORD(hx,x);
+            k = ((hx&0x7ff00000)>>20) - 54;
+            if (n< -50000) return tiny*x;       /*underflow*/
+            }
+        if (k==0x7ff) return x+x;               /* NaN or Inf */
+        k = k+n;
+        if (k >  0x7fe) return huge*copysign(huge,x); /* overflow  */
+        if (k > 0)                              /* normal result */
+            {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
+        if (k <= -54) {
+            if (n > 50000)      /* in case integer overflow in n+k */
+                return huge*copysign(huge,x);   /*overflow*/
+            else
+                return tiny*copysign(tiny,x);   /*underflow*/
         }
-        u.i = (uint64_t)(0x3ff+n)<<52;
-        x = y * u.f;
-
-        return x;
+        k += 54;                                /* subnormal result */
+        SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
+        return x*twom54;
 }