approximateANSIColor: fix possible underflow

2 files changed, 8 insertions, 3 deletions

diff --git a/src/display/term.nim b/src/display/term.nim
index fa3c5e7f..332ecd33 100644
--- a/src/display/term.nim
+++ b/src/display/term.nim
@@ -12,6 +12,7 @@ import config/config
 import data/charset
 import encoding/encoderstream
 import io/window
+import utils/chamath
 import utils/twtstr
 import types/color
 
@@ -217,9 +218,9 @@ proc approximateANSIColor(rgb: RGBColor, exclude = -1): int =
     if i == exclude: continue
     let color = ANSIColorMap[i]
     if color == rgb: return i
-    let x = uint16(color.r - rgb.r) ^ 2
-    let y = uint16(color.g - rgb.b) ^ 2
-    let z = uint16(color.g - rgb.g) ^ 2
+    let x = uint16(absSub(color.r, rgb.r)) ^ 2
+    let y = uint16(absSub(color.g, rgb.b)) ^ 2
+    let z = uint16(absSub(color.g, rgb.g)) ^ 2
     let b = x + y + z
     if n == -1 or b < a:
       n = i
diff --git a/src/utils/chamath.nim b/src/utils/chamath.nim
new file mode 100644
index 00000000..579b7b69
--- /dev/null
+++ b/src/utils/chamath.nim
@@ -0,0 +1,4 @@
+func absSub*(a, b: SomeUnsignedInt): auto {.inline.} =
+  if a > b:
+    return a - b
+  return b - a