lookup tables and binary size difference

[matu3ba]

1. How big are the lookup tables for this? Is there a size difference to the other approaches? I see // Eisel-Lemire tables ~10Kb, so I am curious how much space float parsing for embedded would require in contrast to that.
2. Related, how big is the binary size in comparison?

[tiehuis]

1. We cache 128 bits of precision for pre-computed powers of five from exponents -342 to 308 which is 650 * 16 = 10400 bytes required. You can reduce this if you only need f32 to ~2Kb worth of tables, but I'm not yet sold on this. See also optimized (smaller) lookup table for float (binary32 only) fastfloat/fast_float#99.

Note that the other fairly large user of memory here is the Decimal type. This uses 768 bytes for the digits storage. This space seems reasonable too me, but note that f128 parsing requires a lot more. Specifically the Decimal requires 11563 bytes for storage if parsing to an f128 with full precision. I have yet to fully explore actually using eisel-lemire for f128 parsing but my first revision will likely use the slow-path algorithm only initially.

2. I haven't done any in-depth checks yet but running bloaty on this file with the different parseFloat implementations gives the following:

# build command
zig build-exe test_all_fxx_data.zig -O ReleaseFast && strip test_all_fxx_data

$ bloaty test_all_fxx_data.std
    FILE SIZE        VM SIZE    
 --------------  -------------- 
  67.8%  15.6Ki  44.6%  15.5Ki    .text
   0.0%       0  35.4%  12.3Ki    .bss
  29.0%  6.67Ki  19.0%  6.61Ki    .rodata
   1.5%     344   1.0%     344    [LOAD #1 [R]]
   0.7%     163   0.0%       0    .comment
   0.5%     128   0.0%       0    [ELF Headers]
   0.4%     103   0.0%       0    .shstrtab
   0.1%      15   0.0%       0    [Unmapped]
 100.0%  23.0Ki 100.0%  34.8Ki    TOTAL

bloaty test_all_fxx_data.new
    FILE SIZE        VM SIZE    
 --------------  -------------- 
  58.2%  26.9Ki  46.3%  26.8Ki    .text
  40.2%  18.6Ki  31.9%  18.5Ki    .rodata
   0.0%       0  21.3%  12.3Ki    .bss
   0.7%     352   0.6%     352    [LOAD #1 [R]]
   0.3%     163   0.0%       0    .comment
   0.3%     128   0.0%       0    [ELF Headers]
   0.2%     103   0.0%       0    .shstrtab
   0.0%       6   0.0%       0    [Unmapped]
 100.0%  46.2Ki 100.0%  58.0Ki    TOTAL

So, a bit larger.

[tiehuis]

There is also this table I forgot about:

zig-parsefloat/Decimal.zig

Line 306 in 1ea6a9a

const table = [_]u16{

[andrewrk]

btw we have the --strip flag fully working now:

zig build-exe test_all_fxx_data.zig -O ReleaseFast --strip

[tiehuis]

See https://github.com/tiehuis/zig-parsefloat/blob/master/SIZE.md.