math: fix tgamma to raise underflow for large negative values

diff --git a/src/math/tgamma.c b/src/math/tgamma.c
index 691e86a..f91af73 100644 (file)
--- a/src/math/tgamma.c
+++ b/src/math/tgamma.c
@@ -137,6 +137,7 @@ double tgamma(double x)
        /* x =< -184: tgamma(x)=+-0 with underflow */
        if (absx >= 184) {
                if (x < 0) {
+                       FORCE_EVAL((float)(0x1p-126/x));
                        if (floor(x) * 0.5 == floor(x * 0.5))
                                return 0;
                        return -0.0;