From: Matthew Fernandez <matthew.fernandez@gmail.com>
Date: Wed, 26 May 2021 15:12:03 +0000 (-0700)
Subject: rephrase some magic numbers in Smyrna into their originating computation
X-Git-Tag: 2.47.3~24^2~2
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=0caa33790c8140b66ac4fbe27701f3c6b984dc83;p=graphviz

rephrase some magic numbers in Smyrna into their originating computation

This removes the use of some double literals with implicit conversion to floats,
squashing some -Wfloat-conversion compiler warnings. It also makes the resulting
code clearer. The compiler constant-folds these at -O1 and above, so there is no
loss of performance. The resulting expressions are slightly different to the
original, but if anything they are a more accurate representation of the intent
here.
---

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 649219744..a62750f33 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- marginally more accurate computations in Smyrna sphere projection
+
 ## [2.47.2] - 2021-05-26
 
 ### Added
diff --git a/cmd/smyrna/trackball.c b/cmd/smyrna/trackball.c
index a49ad5cce..041f1165c 100644
--- a/cmd/smyrna/trackball.c
+++ b/cmd/smyrna/trackball.c
@@ -208,10 +208,10 @@ static float tb_project_to_sphere(float r, float x, float y)
     float d, t, z;
 
     d = hypotf(x, y);
-    if (d < r * 0.70710678118654752440) {	/* Inside sphere */
+    if (d < r * (1.0f / sqrtf(2.0f))) {	/* Inside sphere */
 	z = sqrt(r * r - d * d);
     } else {			/* On hyperbola */
-	t = r / 1.41421356237309504880;
+	t = r / sqrtf(2.0f);
 	z = t * t / d;
     }
     return z;