Add example script printing various decimal formats

examples/formatting-examples.rs

@@ -0,0 +1,66 @@
+
+extern crate bigdecimal;
+extern crate num_traits;
+
+use bigdecimal::BigDecimal;
+
+
+macro_rules! print_varying_values {
+    ($fmt:literal, $exp_range:expr) => {
+        print_varying_values!($fmt, $exp_range, 1);
+    };
+    ($fmt:literal, $exp_range:expr, $value:literal) => {
+        println!("{}:", $fmt);
+        println!("{}×", $value);
+        for exp in $exp_range {
+            let n = BigDecimal::new($value.into(), -exp);
+            let dec_str = format!($fmt, n);
+
+            let f = ($value as f64) * 10f64.powi(exp as i32);
+            let float_str = format!($fmt, f);
+
+            let s = format!("10^{}", exp);
+            println!("{:>7} : {:25} {}", s, dec_str, float_str);
+        }
+        println!("");
+    }
+}
+
+macro_rules! print_varying_formats {
+    ($src:literal) => {
+        let src = $src;
+        let n: BigDecimal = src.parse().unwrap();
+        let f: f64 = src.parse().unwrap();
+
+        println!("{}", src);
+        println!("     {{}} : {:<15} {}", n, f);
+
+        for prec in 0..5 {
+            println!("  {{:.{prec}}} : {:<15.prec$} {:.prec$}", n, f, prec=prec);
+        }
+        println!("");
+    };
+}
+
+fn main() {
+    println!("        | BigDecimal     | f64");
+    println!("        +------------    +-----");
+    print_varying_formats!("1234");
+    print_varying_formats!("1.234");
+    print_varying_formats!(".1234");
+    print_varying_formats!(".00001234");
+    print_varying_formats!(".00000001234");
+    print_varying_formats!("12340");
+    print_varying_formats!("1234e1");
+    print_varying_formats!("1234e10");
+
+
+    print_varying_values!("{}", -20..=20);
+    print_varying_values!("{:e}", -20..=20);
+    print_varying_values!("{:.2e}", -20..=20);
+
+    print_varying_values!("{}", -10..=10, 12345);
+    print_varying_values!("{:e}", -10..=10, 12345);
+    print_varying_values!("{:.2e}", -10..=10, 12345);
+    print_varying_values!("{:.3}", -10..=10, 12345);
+}