math: excess precision fix modf, modff, scalbn, scalbnf

old code was correct only if the result was stored (without the
excess precision) or musl was compiled with -ffloat-store.
now we use STRICT_ASSIGN to work around the issue.
(see note 160 in c11 section 6.8.6.4)

diff --git a/src/math/modf.c b/src/math/modf.c
index de45069..8f337ef 100644 (file)
--- a/src/math/modf.c
+++ b/src/math/modf.c
@@ -1,5 +1,4 @@
-#include <math.h>
-#include <stdint.h>
+#include "libm.h"
 
 double modf(double x, double *iptr)
 {
@@ -33,5 +32,6 @@ double modf(double x, double *iptr)
        }
        u.n &= ~mask;
        *iptr = u.x;
-       return x - *iptr;
+       STRICT_ASSIGN(double, x, x - *iptr);
+       return x;
 }

diff --git a/src/math/modff.c b/src/math/modff.c
index 84d0b82..90caf31 100644 (file)
--- a/src/math/modff.c
+++ b/src/math/modff.c
@@ -1,5 +1,4 @@
-#include <math.h>
-#include <stdint.h>
+#include "libm.h"
 
 float modff(float x, float *iptr)
 {
@@ -33,5 +32,6 @@ float modff(float x, float *iptr)
        }
        u.n &= ~mask;
        *iptr = u.x;
-       return x - *iptr;
+       STRICT_ASSIGN(float, x, x - *iptr);
+       return x;
 }

diff --git a/src/math/scalbn.c b/src/math/scalbn.c
index 42a2b29..003141e 100644 (file)
--- a/src/math/scalbn.c
+++ b/src/math/scalbn.c
@@ -2,8 +2,6 @@
 
 double scalbn(double x, int n)
 {
-       /* make sure result is stored as double on overflow or underflow */
-       volatile double z;
        double scale;
 
        if (n > 1023) {
@@ -13,8 +11,8 @@ double scalbn(double x, int n)
                        x *= 0x1p1023;
                        n -= 1023;
                        if (n > 1023) {
-                               z = x * 0x1p1023;
-                               return z;
+                               STRICT_ASSIGN(double, x, x * 0x1p1023);
+                               return x;
                        }
                }
        } else if (n < -1022) {
@@ -24,12 +22,12 @@ double scalbn(double x, int n)
                        x *= 0x1p-1022;
                        n += 1022;
                        if (n < -1022) {
-                               z = x * 0x1p-1022;
-                               return z;
+                               STRICT_ASSIGN(double, x, x * 0x1p-1022);
+                               return x;
                        }
                }
        }
        INSERT_WORDS(scale, (uint32_t)(0x3ff+n)<<20, 0);
-       z = x * scale;
-       return z;
+       STRICT_ASSIGN(double, x, x * scale);
+       return x;
 }

diff --git a/src/math/scalbnf.c b/src/math/scalbnf.c
index e5c76db..f94b5d5 100644 (file)
--- a/src/math/scalbnf.c
+++ b/src/math/scalbnf.c
@@ -2,8 +2,6 @@
 
 float scalbnf(float x, int n)
 {
-       /* make sure result is stored as double on overflow or underflow */
-       volatile float z;
        float scale;
 
        if (n > 127) {
@@ -13,8 +11,8 @@ float scalbnf(float x, int n)
                        x *= 0x1p127f;
                        n -= 127;
                        if (n > 127) {
-                               z = x * 0x1p127f;
-                               return z;
+                               STRICT_ASSIGN(float, x, x * 0x1p127f);
+                               return x;
                        }
                }
        } else if (n < -126) {
@@ -24,12 +22,12 @@ float scalbnf(float x, int n)
                        x *= 0x1p-126f;
                        n += 126;
                        if (n < -126) {
-                               z = x * 0x1p-126f;
-                               return z;
+                               STRICT_ASSIGN(float, x, x * 0x1p-126f);
+                               return x;
                        }
                }
        }
        SET_FLOAT_WORD(scale, (uint32_t)(0x7f+n)<<23);
-       z = x * scale;
-       return z;
+       STRICT_ASSIGN(float, x, x * scale);
+       return x;
 }