elf.h: add ELFCOMPRESS_ZSTD

[musl] / src / math / scalbn.c

diff --git a/src/math/scalbn.c b/src/math/scalbn.c
index c9c7af8..182f561 100644 (file)
--- a/src/math/scalbn.c
+++ b/src/math/scalbn.c
@@ -1,28 +1,33 @@
-#include "libm.h"
+#include <math.h>
+#include <stdint.h>
 
 double scalbn(double x, int n)
 {
-       double scale;
+       union {double f; uint64_t i;} u;
+       double_t y = x;
 
        if (n > 1023) {
-               x *= 0x1p1023;
+               y *= 0x1p1023;
                n -= 1023;
                if (n > 1023) {
-                       x *= 0x1p1023;
+                       y *= 0x1p1023;
                        n -= 1023;
                        if (n > 1023)
-                               return x * 0x1p1023;
+                               n = 1023;
                }
        } else if (n < -1022) {
-               x *= 0x1p-1022;
-               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) {
-                       x *= 0x1p-1022;
-                       n += 1022;
+                       y *= 0x1p-1022 * 0x1p53;
+                       n += 1022 - 53;
                        if (n < -1022)
-                               return x * 0x1p-1022;
+                               n = -1022;
                }
        }
-       INSERT_WORDS(scale, (uint32_t)(0x3ff+n)<<20, 0);
-       return x * scale;
+       u.i = (uint64_t)(0x3ff+n)<<52;
+       x = y * u.f;
+       return x;
 }