`base64` implementation almost 8x slower than GNU for some large files

[BAMF0]

I benchmarked the uutils version against the GNU version of base64 using hyperfine and noticed that there was a significant difference in performance for some large files.

• OS release: Ubuntu Questing Quokka (development branch) 25.10
• GNU coreutils version: 9.5-1ubuntu2+0.0.0~ubuntu20
• uutils coreutils version: 0.1.0

Reproduce

Generate two large files:

• oneline_4G.txt - a single line file consisting of a sequence of A's (4GB in size)

dd if=/dev/zero bs=1M count=4096 status=progress | tr '\0' 'A' |
head -c 4294967295 > oneline_4G.txt && echo >> oneline_4G.txt

• truncated_4G_file - a truncated file (4GB in size)

truncate -s 4G truncated_4G_file

---

Run hyperfine on oneline_4G.txt:

hyperfine 'base64 oneline_4G.txt' 'coreutils base64 oneline_4G.txt' -N --warmup 3

Output

Benchmark 1: base64 oneline_4G.txt
  Time (mean ± σ):      2.461 s ±  0.037 s    [User: 2.067 s, System: 0.394 s]
  Range (min … max):    2.416 s …  2.525 s    10 runs
 
Benchmark 2: coreutils base64 oneline_4G.txt
  Time (mean ± σ):     19.556 s ±  0.571 s    [User: 17.923 s, System: 1.632 s]
  Range (min … max):   18.475 s … 20.434 s    10 runs
 
Summary
  base64 oneline_4G.txt ran
    7.95 ± 0.26 times faster than coreutils base64 oneline_4G.txt

Run hyperfine on truncated_4G_file:

hyperfine 'base64 truncated_4G_file' 'coreutils base64 truncated_4G_file' -N --warmup 3

Output

Benchmark 1: base64 truncated_4G_file
  Time (mean ± σ):      2.449 s ±  0.036 s    [User: 2.044 s, System: 0.405 s]
  Range (min … max):    2.405 s …  2.505 s    10 runs
 
Benchmark 2: coreutils base64 truncated_4G_file
  Time (mean ± σ):     19.451 s ±  0.493 s    [User: 17.829 s, System: 1.621 s]
  Range (min … max):   18.612 s … 20.271 s    10 runs
 
Summary
  base64 truncated_4G_file ran
    7.94 ± 0.23 times faster than coreutils base64 truncated_4G_file

Reference Machine

• OS: Ubuntu Questing Quokka (development branch) 25.10
• Hardware Model: Lenovo Legion Slim 5 16IRH8
• Processor: 13th Gen Intel® Core™ i7-13620H × 16
• Memory: DDR5 16.0 GiB @ 5600 MT/s

[sylvestre]

I have different results:

hyperfine '/usr/bin/base64 /tmp/oneline_4G.txt' './target/release/coreutils base64 /tmp/oneline_4G.txt' -N --warmup 3
Benchmark 1: /usr/bin/base64 /tmp/oneline_4G.txt
  Time (mean ± σ):      5.092 s ±  0.163 s    [User: 4.060 s, System: 1.031 s]
  Range (min … max):    4.924 s …  5.385 s    10 runs

Benchmark 2: ./target/release/coreutils base64 /tmp/oneline_4G.txt
  Time (mean ± σ):      5.964 s ±  0.167 s    [User: 4.268 s, System: 1.695 s]
  Range (min … max):    5.775 s …  6.359 s    10 runs

Summary
  /usr/bin/base64 /tmp/oneline_4G.txt ran
    1.17 ± 0.05 times faster than ./target/release/coreutils base64 /tmp/oneline_4G.txt