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Clarify compile-time benchmark results

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Victor Zverovich 2026-09-06 10:25:41 -07:00
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@ -202,40 +202,39 @@ magnitude slower than the other methods.
## Compile time and code bloat
The script [bloat-test.py][test] from [format-benchmark][bench] tests compile
time and code bloat for nontrivial projects. It generates 100 translation units
and uses `printf()` or its alternative five times in each to simulate a
medium-sized project. The resulting executable size and compile time on an
Apple M5 Max running macOS 26.6.2 with Apple Clang 21.0.0
(clang-2100.1.1.101), taking the best of three runs, are shown in the following
tables.
The script [bloat-test.py][test] from [format-benchmark][bench] measures the
compile-time and code-size overhead each formatting method adds to application
code. It generates 100 translation units and uses `printf` or its alternative
five times in each to simulate a medium-sized project. Library and module build
costs are excluded. Results on an Apple M5 Max running macOS 26.6.2 with
Apple Clang 21.0.0 (clang-2100.1.1.101), taking the best of three runs, are
shown in the following tables.
[test]: https://github.com/fmtlib/format-benchmark/blob/master/bloat-test.py
[bench]: https://github.com/fmtlib/format-benchmark
**Optimized build (-O3)**
| Method | Compile Time, s | Executable size, KiB | Stripped size, KiB |
|--------------------------|-----------------|----------------------|--------------------|
| printf | 1.6 | 54 | 50 |
| IOStreams | 25.5 | 98 | 84 |
| {fmt} 12.2 (non-modular) | 5.1 | 54 | 50 |
| {fmt} 12.2 (modular) | 3.7 | 59 | 50 |
| Boost Format 1.92 | 49.1 | 517 | 317 |
| Method | Compile time, s | Binary size, KiB | Stripped size, KiB |
|--------------------|----------------:|-----------------:|-------------------:|
| printf | 1.6 | 54 | 50 |
| IOStreams | 25.5 | 98 | 84 |
| fmt 12.2 (headers) | 5.1 | 54 | 50 |
| fmt 12.2 (module) | 3.7 | 59 | 50 |
| Boost Format 1.92 | 49.1 | 517 | 317 |
Modular {fmt} is faster to compile than non-modular {fmt}, and both are
comparable to `printf` in terms of per-call binary size (within a rounding error
on this system).
Using modular {fmt} reduces optimized application-code compile time by 27%
without changing the reported stripped binary size.
**Non-optimized build**
| Method | Compile Time, s | Executable size, KiB | Stripped size, KiB |
|--------------------------|-----------------|----------------------|--------------------|
| printf | 1.6 | 54 | 50 |
| IOStreams | 26.0 | 88 | 68 |
| {fmt} 12.2 (non-modular) | 4.9 | 87 | 84 |
| {fmt} 12.2 (modular) | 3.2 | 77 | 68 |
| Boost Format 1.92 | 35.7 | 741 | 431 |
| Method | Compile time, s | Binary size, KiB | Stripped size, KiB |
|--------------------|----------------:|-----------------:|-------------------:|
| printf | 1.6 | 54 | 50 |
| IOStreams | 26.0 | 88 | 68 |
| fmt 12.2 (headers) | 4.9 | 87 | 84 |
| fmt 12.2 (module) | 3.2 | 77 | 68 |
| Boost Format 1.92 | 35.7 | 741 | 431 |
`libc`, `libc++`, `libfmt`, and `libfmt-module` were linked as shared libraries
to compare formatting function overhead only. Boost Format is header-only.