From 4e1e25646161599368f6d7be188e87c072dfea77 Mon Sep 17 00:00:00 2001
From: Austen Adler <agadler@austenadler.com>
Date: Thu, 13 May 2021 22:19:39 -0400
Subject: [PATCH] Fix engineering formatting

---
 src/main.rs | 46 ++++++++++++++++++++++++++++++++--------------
 1 file changed, 32 insertions(+), 14 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 0221937..db1fbc5 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -404,13 +404,18 @@ fn fmt_scientific(f: f64, precision: usize) -> String {
     };
 
     let sign = if !ret.starts_with('-') { " " } else { "" };
-    format!("{}{}E{}{:0>pad$}", sign, ret, exp_sign, exp, pad = 2)
+    format!("{}{} E{}{:0>pad$}", sign, ret, exp_sign, exp, pad = 2)
 }
 
 fn fmt_engineering(f: f64, precision: usize) -> String {
     // Format the string so the first digit is always in the first column, and remove '.'. Requested precision + 2 to account for using 1, 2, or 3 digits for the whole portion of the string
     // 1,000 => 1000E3
-    let all = format!(" {:.precision$E}", f, precision = precision + 2).replacen(".", "", 1);
+    let all = format!(" {:.precision$E}", f, precision = precision)
+        // Remove . since it can be moved
+        .replacen(".", "", 1)
+        // Add 00E before E here so the length is enough for slicing below
+        .replacen("E", "00E", 1);
+    println!("{}", all);
     // Extract mantissa and the string representation of the exponent. Unwrap should be safe as formatter will insert E
     // 1000E3 => (1000, E3)
     let (num_str, exp_str) = all.split_at(all.find('E').unwrap());
@@ -471,20 +476,27 @@ mod tests {
     fn test_fmt_scientific() {
         for (f, p, s) in vec![
             // Basic
-            (1.0, 0, " 1E+00"),
-            (-1.0, 0, "-1E+00"),
-            (100.0, 0, " 1E+02"),
-            (0.1, 0, " 1E-01"),
-            (0.01, 0, " 1E-02"),
-            (-0.1, 0, "-1E-01"),
+            (1.0, 0, " 1 E+00"),
+            (-1.0, 0, "-1 E+00"),
+            (100.0, 0, " 1 E+02"),
+            (0.1, 0, " 1 E-01"),
+            (0.01, 0, " 1 E-02"),
+            (-0.1, 0, "-1 E-01"),
             // i
-            (1.0, 0, " 1E+00"),
+            (1.0, 0, " 1 E+00"),
             // Precision
-            (-0.123456789, 3, "-1.235E-01"),
-            (-0.123456789, 2, "-1.23E-01"),
-            (-0.123456789, 2, "-1.23E-01"),
-            (-1e99, 2, "-1.00E+99"),
-            (-1e100, 2, "-1.00E+100"),
+            (-0.123456789, 3, "-1.235 E-01"),
+            (-0.123456789, 2, "-1.23 E-01"),
+            (-0.123456789, 2, "-1.23 E-01"),
+            (-1e99, 2, "-1.00 E+99"),
+            (-1e100, 2, "-1.00 E+100"),
+            // Rounding
+            (0.5, 2, " 5.00 E-01"),
+            (0.5, 1, " 5.0 E-01"),
+            (0.5, 0, " 5 E-01"),
+            (1.5, 2, " 1.50 E+00"),
+            (1.5, 1, " 1.5 E+00"),
+            (1.5, 0, " 2 E+00"),
         ] {
             assert_eq!(fmt_scientific(f, p), s);
         }
@@ -526,6 +538,12 @@ mod tests {
             (0.001, 2, "   1.00 E-03"),
             (0.0001, 2, " 100.00 E-06"),
             // Rounding
+            (0.5, 2, " 500.00 E-03"),
+            (0.5, 1, " 500.0 E-03"),
+            (0.5, 0, " 500. E-03"),
+            (1.5, 2, "   1.50 E+00"),
+            (1.5, 1, "   1.5 E+00"),
+            (1.5, 0, "   2. E+00"),
         ] {
             assert_eq!(fmt_engineering(f, c), s);
         }