math: fix tgamma to raise underflow for large negative values

diff --git a/src/math/tgamma.c b/src/math/tgamma.c
index 691e86a4bbf504373780e8a4ca24fa523cbfd676..f91af735e7e9eff9a4aac43d2d722803795c5fd6 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;