expand: improve the performances - 1.80 faster than GNU

sylvestre · sylvestre · commit fb5f4d8c2812 · 2025-10-05T10:27:46.000+02:00
diff --git a/src/uu/expand/src/expand.rs b/src/uu/expand/src/expand.rs
@@ -358,6 +358,15 @@ fn expand_line(
 ) -> std::io::Result<()> {
     use self::CharType::{Backspace, Other, Tab};
 
+    // Fast path: if there are no tabs, backspaces, and (in UTF-8 mode or no carriage returns),
+    // we can write the buffer directly without character-by-character processing
+    if !buf.contains(&b'\t') && !buf.contains(&b'\x08') && (options.uflag || !buf.contains(&b'\r'))
+    {
+        output.write_all(buf)?;
+        buf.truncate(0);
+        return Ok(());
+    }
+
     let mut col = 0;
     let mut byte = 0;
     let mut init = true;
@@ -435,7 +444,6 @@ fn expand_line(
         byte += nbytes; // advance the pointer
     }
 
-    output.flush()?;
     buf.truncate(0); // clear the buffer
 
     Ok(())
@@ -471,6 +479,10 @@ fn expand(options: &Options) -> UResult<()> {
             }
         }
     }
+    // Flush once at the end
+    output
+        .flush()
+        .map_err_context(|| translate!("expand-error-failed-to-write-output"))?;
     Ok(())
 }
 

Original file line number	Diff line number	Diff line change
`@@ -358,6 +358,15 @@ fn expand_line(`
`358`	`358`	`) -> std::io::Result<()> {`
`359`	`359`	`use self::CharType::{Backspace, Other, Tab};`
`360`	`360`
	`361`	`+ // Fast path: if there are no tabs, backspaces, and (in UTF-8 mode or no carriage returns),`
	`362`	`+ // we can write the buffer directly without character-by-character processing`
	`363`	`+ if !buf.contains(&b'\t') && !buf.contains(&b'\x08') && (options.uflag \|\| !buf.contains(&b'\r'))`
	`364`	`+ {`
	`365`	`+ output.write_all(buf)?;`
	`366`	`+ buf.truncate(0);`
	`367`	`+ return Ok(());`
	`368`	`+ }`
	`369`	`+`
`361`	`370`	`let mut col = 0;`
`362`	`371`	`let mut byte = 0;`
`363`	`372`	`let mut init = true;`
`@@ -435,7 +444,6 @@ fn expand_line(`
`435`	`444`	`byte += nbytes; // advance the pointer`
`436`	`445`	`}`
`437`	`446`
`438`		`- output.flush()?;`
`439`	`447`	`buf.truncate(0); // clear the buffer`
`440`	`448`
`441`	`449`	`Ok(())`
`@@ -471,6 +479,10 @@ fn expand(options: &Options) -> UResult<()> {`
`471`	`479`	`}`
`472`	`480`	`}`
`473`	`481`	`}`
	`482`	`+ // Flush once at the end`
	`483`	`+ output`
	`484`	`+ .flush()`
	`485`	`+ .map_err_context(\|\| translate!("expand-error-failed-to-write-output"))?;`
`474`	`486`	`Ok(())`
`475`	`487`	`}`
`476`	`488`