Attempt to optimize computing the length of a TLV's length (#561)

alex · web-flow · commit ecbbdf637240 · 2025-06-22T15:16:05.000-07:00
diff --git a/src/writer.rs b/src/writer.rs
@@ -73,13 +73,7 @@ impl WriteBuf {
 }
 
 fn _length_length(length: usize) -> u8 {
-    let mut i = length;
-    let mut num_bytes = 1;
-    while i > 255 {
-        num_bytes += 1;
-        i >>= 8;
-    }
-    num_bytes
+    (usize::BITS - length.leading_zeros()).div_ceil(8) as u8
 }
 
 /// Calculate the number of bytes needed to encode a length field for the given content length.

Original file line number	Diff line number	Diff line change
`@@ -73,13 +73,7 @@ impl WriteBuf {`
`73`	`73`	`}`
`74`	`74`
`75`	`75`	`fn _length_length(length: usize) -> u8 {`
`76`		`- let mut i = length;`
`77`		`- let mut num_bytes = 1;`
`78`		`- while i > 255 {`
`79`		`- num_bytes += 1;`
`80`		`- i >>= 8;`
`81`		`- }`
`82`		`- num_bytes`
	`76`	`+ (usize::BITS - length.leading_zeros()).div_ceil(8) as u8`
`83`	`77`	`}`
`84`	`78`
`85`	`79`	`/// Calculate the number of bytes needed to encode a length field for the given content length.`