perf: parse fractional byte sizes exactly

CHANGELOG.md

@@ -4,6 +4,10 @@ All significant changes to this software be documented in this file.
 
 ## Unreleased
 
+### Bug fixes
+
+* Parse arbitrarily precise fractional byte sizes without double rounding or false overflow.
+
 ## v0.3.0 (2026-06-28)
 
 ### Breaking changes

bsize/Cargo.toml

@@ -42,11 +42,16 @@ macroweave = "0.1.0"
 serde_core = { version = "1", default-features = false, optional = true }
 
 [dev-dependencies]
+divan = "0.1.21"
 insta = { version = "1.47.2" }
 quickcheck = { version = "1.0.0" }
 serde = { version = "1.0.228", features = ["derive"] }
 serde_json = { version = "1.0.150" }
 toml = { version = "1.1.2" }
 
+[[bench]]
+harness = false
+name = "parse"
+
 [lints]
 workspace = true

bsize/benches/parse.rs

@@ -0,0 +1,59 @@
+// Copyright 2026 FastLabs Developers
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::fmt;
+
+use bsize::BSize64;
+use bsize::ParseError;
+
+#[derive(Clone, Copy)]
+struct ParseCase {
+    name: &'static str,
+    input: &'static str,
+}
+
+impl fmt::Display for ParseCase {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(self.name)
+    }
+}
+
+const fn case(name: &'static str, input: &'static str) -> ParseCase {
+    ParseCase { name, input }
+}
+
+const CASES: [ParseCase; 10] = [
+    case("plain", "42"),
+    case("decimal-unit", "42 MB"),
+    case("binary-unit", "1 KiB"),
+    case("fraction", "1.5 MiB"),
+    case("small-fraction", "0.0025 KB"),
+    case("grouped", "1_234_567_890"),
+    case("u64-max", "18_446_744_073_709_551_615"),
+    case("high-precision-decimal", "1.84467440737095516145 EB"),
+    case(
+        "high-precision-binary",
+        "0.0000000000000000004336808689942017736029811203479766845703125 EiB",
+    ),
+    case("malformed", "not-a-size"),
+];
+
+fn main() {
+    divan::main();
+}
+
+#[divan::bench(args = CASES, sample_size = 1024)]
+fn parse(case: ParseCase) -> Result<BSize64, ParseError> {
+    divan::black_box(case.input).parse()
+}