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Int overflow check with a faster approach #394

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632cc97
detect uint64 overflow that wraps past min_safe in parse_int_string
sahvx655-wq Jun 13, 2026
a7249f8
replace checked re-parse with O(1) simdjson-style overflow check
lemire Jun 14, 2026
fd970ab
updating visual studio
lemire Jun 14, 2026
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4 changes: 2 additions & 2 deletions .github/workflows/vs17-arm-ci.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -10,8 +10,8 @@ jobs:
fail-fast: false
matrix:
include:
- {gen: Visual Studio 17 2022, arch: ARM64, cfg: Release}
- {gen: Visual Studio 17 2022, arch: ARM64, cfg: Debug}
- {gen: Visual Studio 18 2026, arch: ARM64, cfg: Release}
- {gen: Visual Studio 18 2026, arch: ARM64, cfg: Debug}
steps:
- name: checkout
uses: actions/checkout@v6.0.2
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8 changes: 4 additions & 4 deletions .github/workflows/vs17-ci.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -10,10 +10,10 @@ jobs:
fail-fast: false
matrix:
include:
- {gen: Visual Studio 17 2022, arch: Win32, cfg: Release}
#- {gen: Visual Studio 17 2022, arch: Win32, cfg: Debug}
- {gen: Visual Studio 17 2022, arch: x64, cfg: Release}
- {gen: Visual Studio 17 2022, arch: x64, cfg: Debug}
- {gen: Visual Studio 18 2026, arch: Win32, cfg: Release}
#- {gen: Visual Studio 18 2026, arch: Win32, cfg: Debug}
- {gen: Visual Studio 18 2026, arch: x64, cfg: Release}
- {gen: Visual Studio 18 2026, arch: x64, cfg: Debug}
steps:
- name: checkout
uses: actions/checkout@v6.0.2
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8 changes: 4 additions & 4 deletions .github/workflows/vs17-clang-ci.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -10,10 +10,10 @@ jobs:
fail-fast: false
matrix:
include:
- {gen: Visual Studio 17 2022, arch: Win32, cfg: Release}
- {gen: Visual Studio 17 2022, arch: Win32, cfg: Debug}
- {gen: Visual Studio 17 2022, arch: x64, cfg: Release}
- {gen: Visual Studio 17 2022, arch: x64, cfg: Debug}
- {gen: Visual Studio 18 2026, arch: Win32, cfg: Release}
- {gen: Visual Studio 18 2026, arch: Win32, cfg: Debug}
- {gen: Visual Studio 18 2026, arch: x64, cfg: Release}
- {gen: Visual Studio 18 2026, arch: x64, cfg: Debug}
steps:
- name: checkout
uses: actions/checkout@v6.0.2
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8 changes: 4 additions & 4 deletions .github/workflows/vs17-cxx20.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -10,10 +10,10 @@ jobs:
fail-fast: false
matrix:
include:
- {gen: Visual Studio 17 2022, arch: Win32, cfg: Release}
- {gen: Visual Studio 17 2022, arch: Win32, cfg: Debug}
- {gen: Visual Studio 17 2022, arch: x64, cfg: Release}
- {gen: Visual Studio 17 2022, arch: x64, cfg: Debug}
- {gen: Visual Studio 18 2026, arch: Win32, cfg: Release}
- {gen: Visual Studio 18 2026, arch: Win32, cfg: Debug}
- {gen: Visual Studio 18 2026, arch: x64, cfg: Release}
- {gen: Visual Studio 18 2026, arch: x64, cfg: Debug}
steps:
- name: checkout
uses: actions/checkout@v6.0.2
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24 changes: 21 additions & 3 deletions include/fast_float/ascii_number.h
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Expand Up @@ -781,9 +781,27 @@ parse_int_string(UC const *p, UC const *pend, T &value,
}
// this check can be eliminated for all other types, but they will all require
// a max_digits(base) equivalent
if (digit_count == max_digits && i < min_safe_u64(base)) {
answer.ec = std::errc::result_out_of_range;
return answer;
if (digit_count == max_digits) {
// At the max_digits boundary the accumulator `i` may have wrapped around
// 2^64. A plain `i < min_safe_u64(base)` test is not sufficient: for any
// base whose max_digits-length range exceeds 2^64 (base 10 reaches
// ~5.4 * 2^64 at 20 digits) the value can wrap a whole multiple of 2^64 and
// land back above min_safe, slipping through. Decide exactly in O(1) using
// the leading digit, following the approach used in simdjson:
// ms == min_safe_u64(base) == base^(max_digits-1), the smallest
// max_digits-length value.
// dmax == the largest leading digit whose number can still fit in u64.
// The leading-digit band [d*ms, (d+1)*ms) has width ms < 2^64, so within
// the single band where d == dmax the value straddles 2^64 at most once,
// and a single threshold separates wrapped from non-wrapped values. A
// leading digit above dmax always overflows; below dmax always fits.
uint64_t const ms = min_safe_u64(base);
uint64_t const dmax = (std::numeric_limits<uint64_t>::max)() / ms;
uint64_t const lead = ch_to_digit(*start_digits);
if (lead > dmax || (lead == dmax && i < dmax * ms)) {
answer.ec = std::errc::result_out_of_range;
return answer;
}
}

// check other types overflow
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