math: add fma TODO comments about the underflow issue

[musl] / src / math / fmal.c

diff --git a/src/math/fmal.c b/src/math/fmal.c
index be64f14..87e30fc 100644 (file)
--- a/src/math/fmal.c
+++ b/src/math/fmal.c
@@ -162,6 +162,7 @@ static inline struct dd dd_mul(long double a, long double b)
  */
 long double fmal(long double x, long double y, long double z)
 {
+       #pragma STDC FENV_ACCESS ON
        long double xs, ys, zs, adj;
        struct dd xy, r;
        int oround;
@@ -261,6 +262,8 @@ long double fmal(long double x, long double y, long double z)
                /*
                 * There is no need to worry about double rounding in directed
                 * rounding modes.
+                * TODO: underflow is not raised correctly, example in downward rounding:
+                * fmal(0x1.0000000001p-16000L, 0x1.0000000001p-400L, -0x1p-16440L)
                 */
                fesetround(oround);
                adj = r.lo + xy.lo;