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Khem Raj
9bfe6f0ea9
float_as_int_without_noise() returns early when the floored value fits in a long, checking it with floor_val == static_cast<long>(floor_val). For values outside the range of long the conversion is undefined behavior; clang -O2 folds the round trip into "floor_val is integral", which is always true, so the denoising is skipped: FAIL: tests/test_fastnumbers_examples.py:test_try_real FAIL: tests/test_fastnumbers_examples.py:test_try_forceint assert 3452999999999999737856 == 3453000000000000000000 Add a patch that only does the conversion when the value is in range. A reduced reproducer returns the wrong answer with the recipe's clang++ at -O2 and the right one with the fix (and with -O0 or gcc). AI-Generated: Uses Claude Code Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>
47 lines
1.9 KiB
Diff
47 lines
1.9 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Khem Raj <khem.raj@oss.qualcomm.com>
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Date: Sat, 12 Sep 2026 00:00:00 -0700
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Subject: [PATCH] parser: avoid undefined double to long conversion in
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float_as_int_without_noise
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float_as_int_without_noise() returns early when the floored value fits
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in a long:
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if (floor_val == static_cast<long>(floor_val))
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For values outside the range of long (e.g. 3.453e21) the conversion is
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undefined behavior. clang (-O2) takes advantage of that and folds the
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round trip into "floor_val is integral", which is always true, so the
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denoising is skipped and try_real(3.453e21, denoise=True) returns
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3452999999999999737856 instead of 3453000000000000000000:
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tests/test_fastnumbers_examples.py::test_try_real FAILED
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tests/test_fastnumbers_examples.py::test_try_forceint FAILED
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Only do the conversion when the value is within the range of long.
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Upstream-Status: Pending
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Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>
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---
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src/cpp/parser.cpp | 8 +++++++-
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1 file changed, 7 insertions(+), 1 deletion(-)
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--- a/src/cpp/parser.cpp
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+++ b/src/cpp/parser.cpp
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@@ -92,8 +92,14 @@
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// If the given float can fit a C long without loss then no need
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// to go through the below rounding steps.
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+ // Converting a double that is outside the range of long is undefined
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+ // behavior, and clang uses that to fold this check into "floor_val is
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+ // integral", which is always true and skips the denoising below for large
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+ // values. Make sure the value is in range before converting.
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const double floor_val = std::floor(val);
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- if (floor_val == static_cast<long>(floor_val)) {
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+ constexpr double long_limit = -static_cast<double>(std::numeric_limits<long>::min());
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+ if (floor_val >= -long_limit && floor_val < long_limit
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+ && floor_val == static_cast<long>(floor_val)) {
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return val_int;
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}
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