From ecffc89f29a7d80c362935f9af66deae213fcabc Mon Sep 17 00:00:00 2001
From: Rose Hogenson <rosehogenson@posteo.net>
Date: Tue, 28 May 2024 18:12:22 -0700
Subject: Fix a performance issue in the UI.

---
 src/eval.rs | 42 ++++++++++++++++++++++++++++++++----------
 1 file changed, 32 insertions(+), 10 deletions(-)

(limited to 'src/eval.rs')

diff --git a/src/eval.rs b/src/eval.rs
index e07bec2..470bae6 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -194,19 +194,41 @@ impl Num {
     }
 }
 
-fn format_float(f: f64) -> String {
-    let mut s = format!("{f:.7}");
-    while let Some(b'0') = s.as_bytes().get(s.len() - 1) {
-        s.truncate(s.len() - 1);
-    }
-    s
-}
-
 impl Display for Num {
     fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), std::fmt::Error> {
         match self {
-            Num::Int(n) => write!(f, "{n}"),
-            Num::Float(n) => write!(f, "{}", format_float(*n)),
+            Num::Int(n) => {
+                if n.bits() < 100 {
+                    return write!(f, "{n}");
+                }
+                let buf = format!("{n}");
+                let rounding_factor = BigInt::from(10).pow(buf.len() - 8);
+                let (mut rounded, rem) = n.div_mod_floor(&rounding_factor);
+                match rem.cmp(&(rounding_factor / 2)) {
+                    Ordering::Greater => rounded += 1,
+                    Ordering::Equal if rounded.is_odd() => rounded += 1,
+                    _ => (),
+                }
+                let rounded_str = format!("{rounded}");
+                write!(
+                    f,
+                    "{}.{}e{}",
+                    &rounded_str[..1],
+                    &rounded_str[1..],
+                    buf.len() - 1
+                )
+            }
+            Num::Float(n) => {
+                let n = *n;
+                if !(-1e30..=1e30).contains(&n) {
+                    return write!(f, "{n:.7e}");
+                }
+                let mut buf = format!("{n:.7}");
+                while let Some(b'0') = buf.as_bytes().get(buf.len() - 1) {
+                    buf.truncate(buf.len() - 1);
+                }
+                write!(f, "{buf}")
+            }
         }
     }
 }
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