Optimize IntoLinear table generation as detailed by okaneco

palette/build/lut.rs

@@ -144,7 +144,8 @@ pub fn build_transfer_fn(writer: &mut File) {
 }
 
 fn gen_into_linear_lut_u8(writer: &mut File, entries: &[LutEntryU8]) {
-    use std::io::Write;
+    use std::fmt::Write as _;
+    use std::io::Write as _;
 
     for LutEntryU8 {
         fn_type,
@@ -155,20 +156,24 @@ fn gen_into_linear_lut_u8(writer: &mut File, entries: &[LutEntryU8]) {
     {
         let table_size = 1 << 8;
         let mut table = Vec::new();
-        for i in 0..table_size {
+        // Handle integer floats printing without decimal
+        table.extend_from_slice(b"\t0.0,\n");
+
+        let mut float_string = String::new();
+
+        for i in 1..(table_size - 1) {
             let encoded = (i as f64) / ((table_size - 1) as f64);
             let linear = into_linear(encoded);
-            // Handle integer floats printing without decimal
-            let float_string = if linear <= 0.0 {
-                "\t0.0,\n".to_owned()
-            } else if linear >= 1.0 {
-                "\t1.0,\n".to_owned()
-            } else {
-                format!("\t{linear},\n")
-            };
+
+            writeln!(&mut float_string, "\t{linear},").unwrap();
             table.extend_from_slice(float_string.as_bytes());
+
+            float_string.clear();
         }
 
+        // Handle integer floats printing without decimal
+        table.extend_from_slice(b"\t1.0,\n");
+
         let table_name = format!("{fn_type_uppercase}_U8_TO_F64");
         writeln!(writer, "const {table_name}: [f64; {table_size}] = [").unwrap();
         writer.write_all(&table).unwrap();
@@ -200,7 +205,8 @@ fn gen_into_linear_lut_u8(writer: &mut File, entries: &[LutEntryU8]) {
 
 #[cfg(feature = "prophoto_lut")]
 fn gen_into_linear_lut_u16(writer: &mut File, entries: &[LutEntryU16]) {
-    use std::io::Write;
+    use std::fmt::Write as _;
+    use std::io::Write as _;
 
     for LutEntryU16 {
         fn_type,
@@ -211,20 +217,24 @@ fn gen_into_linear_lut_u16(writer: &mut File, entries: &[LutEntryU16]) {
     {
         let table_size = 1 << 16;
         let mut table = Vec::new();
-        for i in 0..table_size {
+        // Handle integer floats printing without decimal
+        table.extend_from_slice(b"\t0.0,\n");
+
+        let mut float_string = String::new();
+
+        for i in 1..(table_size - 1) {
             let encoded = (i as f64) / ((table_size - 1) as f64);
             let linear = into_linear(encoded);
-            // Handle integer floats printing without decimal
-            let float_string = if linear <= 0.0 {
-                "\t0.0,\n".to_owned()
-            } else if linear >= 1.0 {
-                "\t1.0,\n".to_owned()
-            } else {
-                format!("\t{linear},\n")
-            };
+
+            writeln!(&mut float_string, "\t{linear},").unwrap();
             table.extend_from_slice(float_string.as_bytes());
+
+            float_string.clear();
         }
 
+        // Handle integer floats printing without decimal
+        table.extend_from_slice(b"\t1.0,\n");
+
         let table_name = format!("{fn_type_uppercase}_U16_TO_F64");
         writeln!(writer, "static {table_name}: [f64; {table_size}] = [").unwrap();
         writer.write_all(&table).unwrap();