mirror of
https://github.com/mruby/mruby
synced 2026-06-08 16:11:16 +00:00
Yukihiro "Matz" Matsumoto
9ff1aa9d55
Replace separate float formatting (fmt_fp.c) and parsing (readfloat.c) implementations with a unified fp_uscale.c using 128-bit unrounded scaling. Both mrb_format_float() and mrb_read_float() now share a single pow10 table and uscale() primitive for decimal/binary conversion. This fixes subnormal parsing accuracy (old code returned 0.0 for the smallest subnormals) and corrects %.2f rounding for values like 12345.125. Table size grows from ~5KB to ~11KB in .rodata. Co-authored-by: Claude <noreply@anthropic.com>
69 lines
1.6 KiB
Ruby
Executable File
69 lines
1.6 KiB
Ruby
Executable File
#!/usr/bin/env ruby
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# frozen_string_literal: true
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# Generate pow10 table for mruby unrounded scaling (fp_uscale.c)
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#
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# Uses exact integer arithmetic only.
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# For each p in [-343, 341], computes (hi, lo) such that:
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# 10^p ~= (hi * 2^64 - lo) * 2^pe
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# where pe = floor(p * log2(10)) - 127
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#
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# The 128-bit value pm = hi * 2^64 - lo is in [2^127, 2^128).
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POW10_MIN = -343
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POW10_MAX = 341
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def generate_entry(p)
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if p >= 0
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val = 10**p
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bit_len = val.bit_length
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pe = bit_len - 128
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if pe >= 0
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mask = (1 << pe) - 1
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pm = (val >> pe) + ((val & mask) != 0 ? 1 : 0)
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else
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pm = val << (-pe)
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end
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else
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abs_p = -p
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denom = 10**abs_p
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# pe = floor(p * log2(10)) - 127
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# Ruby's integer division of negative numbers does floor division
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pe_est = (p * 108853 >> 15) - 127
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numerator = 1 << (-pe_est)
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pm = (numerator + denom - 1) / denom
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# Adjust pe if pm is out of range [2^127, 2^128)
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while pm >= (1 << 128)
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pe_est += 1
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numerator = 1 << (-pe_est)
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pm = (numerator + denom - 1) / denom
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end
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while pm < (1 << 127)
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pe_est -= 1
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numerator = 1 << (-pe_est)
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pm = (numerator + denom - 1) / denom
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end
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end
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raise "pm out of range for p=#{p}: #{pm.bit_length}" unless pm.bit_length == 128
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hi = (pm >> 64) + ((pm & ((1 << 64) - 1)) != 0 ? 1 : 0)
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lo = (hi << 64) - pm
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raise "hi out of range for p=#{p}" unless hi >= (1 << 63) && hi < (1 << 64)
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{ hi: hi, lo: lo }
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end
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def main
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entries = (POW10_MIN..POW10_MAX).map { |p| [p, generate_entry(p)] }
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entries.each do |p, e|
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printf(" {0x%016xULL, 0x%016xULL},\n", e[:hi], e[:lo])
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end
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end
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main
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