math: use '#pragma STDC FENV_ACCESS ON' when fenv is accessed

[musl] / src / math / fma.c

diff --git a/src/math/fma.c b/src/math/fma.c
index 87d450c..17f1cdc 100644 (file)
--- a/src/math/fma.c
+++ b/src/math/fma.c
@@ -41,7 +41,7 @@ static void mul(long double *hi, long double *lo, long double x, long double y)
 
 /*
 assume (long double)(hi+lo) == hi
-return an adjusted hi so that rounding it to double is correct
+return an adjusted hi so that rounding it to double (or less) precision is correct
 */
 static long double adjust(long double hi, long double lo)
 {
@@ -55,17 +55,25 @@ static long double adjust(long double hi, long double lo)
        ulo.x = lo;
        if (uhi.bits.s == ulo.bits.s)
                uhi.bits.m++;
-       else
+       else {
                uhi.bits.m--;
+               /* handle underflow and take care of ld80 implicit msb */
+               if (uhi.bits.m == (uint64_t)-1/2) {
+                       uhi.bits.m *= 2;
+                       uhi.bits.e--;
+               }
+       }
        return uhi.x;
 }
 
+/* adjusted add so the result is correct when rounded to double (or less) precision */
 static long double dadd(long double x, long double y)
 {
        add(&x, &y, x, y);
        return adjust(x, y);
 }
 
+/* adjusted mul so the result is correct when rounded to double (or less) precision */
 static long double dmul(long double x, long double y)
 {
        mul(&x, &y, x, y);
@@ -81,6 +89,7 @@ static int getexp(long double x)
 
 double fma(double x, double y, double z)
 {
+       #pragma STDC FENV_ACCESS ON
        long double hi, lo1, lo2, xy;
        int round, ez, exy;
 
@@ -247,7 +256,7 @@ static inline double add_and_denormalize(double a, double b, int scale)
                        INSERT_WORD64(sum.hi, hibits);
                }
        }
-       return (ldexp(sum.hi, scale));
+       return scalbn(sum.hi, scale);
 }
 
 /*
@@ -298,6 +307,7 @@ static inline struct dd dd_mul(double a, double b)
  */
 double fma(double x, double y, double z)
 {
+       #pragma STDC FENV_ACCESS ON
        double xs, ys, zs, adj;
        struct dd xy, r;
        int oround;
@@ -364,7 +374,7 @@ double fma(double x, double y, double z)
                }
        }
        if (spread <= DBL_MANT_DIG * 2)
-               zs = ldexp(zs, -spread);
+               zs = scalbn(zs, -spread);
        else
                zs = copysign(DBL_MIN, zs);
 
@@ -390,7 +400,7 @@ double fma(double x, double y, double z)
                 */
                fesetround(oround);
                volatile double vzs = zs; /* XXX gcc CSE bug workaround */
-               return (xy.hi + vzs + ldexp(xy.lo, spread));
+               return xy.hi + vzs + scalbn(xy.lo, spread);
        }
 
        if (oround != FE_TONEAREST) {
@@ -400,13 +410,13 @@ double fma(double x, double y, double z)
                 */
                fesetround(oround);
                adj = r.lo + xy.lo;
-               return (ldexp(r.hi + adj, spread));
+               return scalbn(r.hi + adj, spread);
        }
 
        adj = add_adjusted(r.lo, xy.lo);
        if (spread + ilogb(r.hi) > -1023)
-               return (ldexp(r.hi + adj, spread));
+               return scalbn(r.hi + adj, spread);
        else
-               return (add_and_denormalize(r.hi, adj, spread));
+               return add_and_denormalize(r.hi, adj, spread);
 }
 #endif