From bd636471774fda847e2a6eaa92a72600428a16cc Mon Sep 17 00:00:00 2001
From: Carter Schmidt <35572862+Fyrecean@users.noreply.github.com>
Date: Sun, 1 Mar 2026 23:54:47 -0800
Subject: [PATCH] Fix crash when dragging a DragValue through small floats.
 (#7939)

Increased smart_aim `NUM_DECIMALS` from 15 to 16 to fix crash in
`best_in_range_f64`
The f64 value 0.09999999999999995, when multiplied by `scale_factor` and
rounded, becomes 16 digits (999999999999999.5 -> 1000000000000000) and
the leading 1 is clipped off by `to_decimal_string` resulting in all 0s
and triggering the debug_assert! message "Bug in smart aim code"

<!--
Please read the "Making a PR" section of
[`CONTRIBUTING.md`](https://github.com/emilk/egui/blob/main/CONTRIBUTING.md)
before opening a Pull Request!

* Keep your PR:s small and focused.
* The PR title is what ends up in the changelog, so make it descriptive!
* If applicable, add a screenshot or gif.
* If it is a non-trivial addition, consider adding a demo for it to
`egui_demo_lib`, or a new example.
* Do NOT open PR:s from your `master` branch, as that makes it hard for
maintainers to test and add commits to your PR.
* Remember to run `cargo fmt` and `cargo clippy`.
* Open the PR as a draft until you have self-reviewed it and run
`./scripts/check.sh`.
* When you have addressed a PR comment, mark it as resolved.

Please be patient! I will review your PR, but my time is limited!
-->

* Closes <https://github.com/emilk/egui/issues/7747 >
* [x] I have followed the instructions in the PR template
---
 crates/emath/src/smart_aim.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/crates/emath/src/smart_aim.rs b/crates/emath/src/smart_aim.rs
index c1b96ec7b..5d6a3e0fc 100644
--- a/crates/emath/src/smart_aim.rs
+++ b/crates/emath/src/smart_aim.rs
@@ -2,7 +2,7 @@
 
 use crate::fast_midpoint;
 
-const NUM_DECIMALS: usize = 15;
+const NUM_DECIMALS: usize = 16;
 
 /// Find the "simplest" number in a closed range [min, max], i.e. the one with the fewest decimal digits.
 ///
@@ -143,6 +143,10 @@ fn from_decimal_string(s: [u8; NUM_DECIMALS]) -> u64 {
 #[expect(clippy::approx_constant)]
 #[test]
 fn test_aim() {
+    assert_eq!(
+        best_in_range_f64(0.0799999999999996, 0.09999999999999995),
+        0.08,
+    );
     assert_eq!(best_in_range_f64(-0.2, 0.0), 0.0, "Prefer zero");
     assert_eq!(best_in_range_f64(-10_004.23, 3.14), 0.0, "Prefer zero");
     assert_eq!(best_in_range_f64(-0.2, 100.0), 0.0, "Prefer zero");