From e97e873b9ef448aa2796667ba1d0a69ffe2e07e0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Thu, 3 Feb 2022 22:17:10 +0100
Subject: [PATCH] box-drawing: LIGHT ARC: check for sqrt() failures

Closes #914
---
 CHANGELOG.md  |  2 ++
 box-drawing.c | 12 ++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7e0196a8..f9ea4980 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -123,6 +123,8 @@
 * Sixel: large image resizes (triggered by e.g. large repeat counts in
   `DECGRI`) are now truncated instead of ignored.
 * Sixel: a repeat count of 0 in `DECGRI` now emits a single sixel.
+* LIGHT ARC box drawing characters incorrectly rendered
+  platforms (https://codeberg.org/dnkl/foot/issues/914).
 
 
 ### Security
diff --git a/box-drawing.c b/box-drawing.c
index 3f8a38ef..09f16d6a 100644
--- a/box-drawing.c
+++ b/box-drawing.c
@@ -1,6 +1,8 @@
 #include "box-drawing.h"
 
 #include <stdio.h>
+#include <math.h>
+#include <fenv.h>
 #include <errno.h>
 
 #define LOG_MODULE "box-drawing"
@@ -1282,9 +1284,19 @@ draw_box_drawings_light_arc(struct buf *buf, wchar_t wc)
     const int num_samples = height * 16;
 
     for (int i = 0; i < num_samples; i++) {
+        errno = 0;
+        feclearexcept(FE_ALL_EXCEPT);
+
         double y = i / 16.;
         double x = sqrt(a2 * (1. - y * y / b2));
 
+        /* See math_error(7) */
+        if (errno != 0 ||
+            fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW))
+        {
+            continue;
+        }
+
         const int row = round(y);
         const int col = round(x);