X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=qscale.c;h=1b3ab57c0b9bd20a76785d66caac745b445a774c;hb=0f5c62013c0210e1f9806342eb1271674f735d7d;hp=6d529bcb4d1d73c49b314eb036b54915fc7dd258;hpb=85edeac1ae18442aa7dc43074a2e4ddc31b6a731;p=qscale

diff --git a/qscale.c b/qscale.c
index 6d529bc..1b3ab57 100644
--- a/qscale.c
+++ b/qscale.c
@@ -9,11 +9,18 @@
 
 double sinc(double x)
 {
-	// This is bad for very small x, should use power series instead.
-	if (x == 0.0)
-		return 1.0;
-	else
+	static const double eps = 2.22045e-016;
+	static const double cutoff = sqrt(sqrt(eps));
+
+	if (abs(x) < cutoff) {
+		// For small |x|, use Taylor series instead
+		const double x2 = x * x;
+		const double x4 = x2 * x2;
+
+		return 1.0 - x2 / 6.0 + x4 / 120.0;
+	} else {
 		return sin(x) / x;
+	}
 }
 
 double lanczos_tap(double x)