FIX: Format numbers a tad better

I still think there is some way to go, but this is closer to Excel

base/src/formatter/format.rs

@@ -15,7 +15,7 @@ pub struct Formatted {
 
 /// Returns the vector of chars of the fractional part of a *positive* number:
 /// 3.1415926 ==> ['1', '4', '1', '5', '9', '2', '6']
-fn get_fract_part(value: f64, precision: i32) -> Vec<char> {
+fn get_fract_part(value: f64, precision: i32, int_len: usize) -> Vec<char> {
     let b = format!("{:.1$}", value.fract(), precision as usize)
         .chars()
         .collect::<Vec<char>>();
@@ -30,6 +30,12 @@ fn get_fract_part(value: f64, precision: i32) -> Vec<char> {
     if last_non_zero < 2 {
         return vec![];
     }
+    let max_len = if int_len > 15 {
+        2_usize
+    } else {
+        15_usize - int_len + 1
+    };
+    let last_non_zero = usize::min(last_non_zero, max_len + 1);
     b[2..last_non_zero].to_vec()
 }
 
@@ -423,7 +429,7 @@ pub fn format_number(value_original: f64, format: &str, locale: &Locale) -> Form
             if value_abs as i64 == 0 {
                 int_part = vec![];
             }
-            let fract_part = get_fract_part(value_abs, p.precision);
+            let fract_part = get_fract_part(value_abs, p.precision, int_part.len());
             // ln is the number of digits of the integer part of the value
             let ln = int_part.len() as i32;
             // digit count is the number of digit tokens ('0', '?' and '#') to the left of the decimal point

base/src/functions/util.rs

@@ -1,7 +1,10 @@
 #[cfg(feature = "use_regex_lite")]
 use regex_lite as regex;
 
-use crate::{calc_result::CalcResult, expressions::token::is_english_error_string};
+use crate::{
+    calc_result::CalcResult, expressions::token::is_english_error_string,
+    number_format::to_excel_precision,
+};
 
 /// This test for exact match (modulo case).
 ///   * strings are not cast into bools or numbers
@@ -34,6 +37,8 @@ pub(crate) fn values_are_equal(left: &CalcResult, right: &CalcResult) -> bool {
 pub(crate) fn compare_values(left: &CalcResult, right: &CalcResult) -> i32 {
     match (left, right) {
         (CalcResult::Number(value1), CalcResult::Number(value2)) => {
+            let value1 = to_excel_precision(*value1, 15);
+            let value2 = to_excel_precision(*value2, 15);
             if (value2 - value1).abs() < f64::EPSILON {
                 return 0;
             }

base/src/number_format.rs

@@ -112,29 +112,36 @@ pub fn to_precision(value: f64, precision: usize) -> f64 {
 /// ```
 /// This intends to be equivalent to the js: `${parseFloat(value.toPrecision(precision)})`
 /// See ([ecma](https://tc39.es/ecma262/#sec-number.prototype.toprecision)).
-/// FIXME: There has to be a better algorithm :/
 pub fn to_excel_precision_str(value: f64) -> String {
     to_precision_str(value, 15)
 }
+
+pub fn to_excel_precision(value: f64, precision: usize) -> f64 {
+    if !value.is_finite() {
+        return value;
+    }
+
+    let s = format!("{:.*e}", precision.saturating_sub(1), value);
+    s.parse::<f64>().unwrap_or(value)
+}
+
 pub fn to_precision_str(value: f64, precision: usize) -> String {
-    if value.is_infinite() {
-        return "inf".to_string();
+    if !value.is_finite() {
+        if value.is_infinite() {
+            return "inf".to_string();
+        } else {
+            return "NaN".to_string();
+        }
     }
-    if value.is_nan() {
-        return "NaN".to_string();
-    }
-    let exponent = value.abs().log10().floor();
-    let base = value / 10.0_f64.powf(exponent);
-    let base = format!("{0:.1$}", base, precision - 1);
-    let value = format!("{base}e{exponent}").parse::<f64>().unwrap_or({
-        // TODO: do this in a way that does not require a possible error
-        0.0
-    });
+
+    let s = format!("{:.*e}", precision.saturating_sub(1), value);
+    let parsed = s.parse::<f64>().unwrap_or(value);
+
     // I would love to use the std library. There is not a speed concern here
     // problem is it doesn't do the right thing
     // Also ryu is my favorite _modern_ algorithm
     let mut buffer = ryu::Buffer::new();
-    let text = buffer.format(value);
+    let text = buffer.format(parsed);
     // The above algorithm converts 2 to 2.0 regrettably
     if let Some(stripped) = text.strip_suffix(".0") {
         return stripped.to_string();

base/src/test/test_number_format.rs

@@ -8,6 +8,15 @@ fn test_simple_format() {
     assert_eq!(formatted.text, "2.3".to_string());
 }
 
+#[test]
+fn test_maximum_zeros() {
+    let formatted = format_number(1.0 / 3.0, "#,##0.0000000000000000000", "en");
+    assert_eq!(formatted.text, "0.3333333333333330000".to_string());
+
+    let formatted = format_number(1234.0 + 1.0 / 3.0, "#,##0.0000000000000000000", "en");
+    assert_eq!(formatted.text, "1,234.3333333333300000000".to_string());
+}
+
 #[test]
 #[ignore = "not yet implemented"]
 fn test_wrong_locale() {

base/src/test/test_trigonometric.rs

@@ -96,3 +96,14 @@ fn test_fn_tan_pi2() {
     // This is consistent with IEEE 754 but inconsistent with Excel
     assert_eq!(model._get_text("A1"), *"1.63312E+16");
 }
+
+#[test]
+fn test_trigonometric_identity() {
+    let mut model = new_empty_model();
+    model._set("A1", "=COTH(1)*CSCH(1)");
+    model._set("A2", "=COSH(1)/(SINH(1))^2");
+    model._set("A3", "=A1=A2");
+    model.evaluate();
+
+    assert_eq!(model._get_text("A3"), *"TRUE");
+}