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From: Patrick Palka <ppalka@redhat.com>
To: gcc-patches@gcc.gnu.org
Cc: libstdc++@gcc.gnu.org, Patrick Palka <ppalka@redhat.com>
Subject: [PATCH 3/5] libstdc++: Adjust fast_float's over/underflow behavior for conformnace
Date: Mon, 15 Nov 2021 19:25:03 -0500	[thread overview]
Message-ID: <20211116002505.2324582-3-ppalka@redhat.com> (raw)
In-Reply-To: <20211116002505.2324582-1-ppalka@redhat.com>

This makes fast_float handle the situation where std::from_chars is
specified to return result_out_of_range, i.e. when the parsed value
is outside the representable range of the floating-point type.

libstdc++-v3/ChangeLog:

	* src/c++17/fast_float/LOCAL_PATCHES: Update.
	* src/c++17/fast_float/parse_number.h (from_chars_advanced): In
	case of over/underflow, return errc::result_out_of_range and don't
	modify 'value'.
---
 libstdc++-v3/src/c++17/fast_float/LOCAL_PATCHES  |  1 +
 libstdc++-v3/src/c++17/fast_float/parse_number.h | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/libstdc++-v3/src/c++17/fast_float/LOCAL_PATCHES b/libstdc++-v3/src/c++17/fast_float/LOCAL_PATCHES
index e9d7bba6195..1f90f9d1d85 100644
--- a/libstdc++-v3/src/c++17/fast_float/LOCAL_PATCHES
+++ b/libstdc++-v3/src/c++17/fast_float/LOCAL_PATCHES
@@ -1 +1,2 @@
 r12-????
+r12-????
diff --git a/libstdc++-v3/src/c++17/fast_float/parse_number.h b/libstdc++-v3/src/c++17/fast_float/parse_number.h
index 86dea2287b4..57b3585c2fe 100644
--- a/libstdc++-v3/src/c++17/fast_float/parse_number.h
+++ b/libstdc++-v3/src/c++17/fast_float/parse_number.h
@@ -99,6 +99,16 @@ from_chars_result from_chars_advanced(const char *first, const char *last,
   // If we called compute_float<binary_format<T>>(pns.exponent, pns.mantissa) and we have an invalid power (am.power2 < 0),
   // then we need to go the long way around again. This is very uncommon.
   if(am.power2 < 0) { am = digit_comp<T>(pns, am); }
+
+  if((pns.mantissa != 0 && am.mantissa == 0 && am.power2 == 0) || am.power2 == binary_format<T>::infinite_power()) {
+    // In case of over/underflow, return result_out_of_range and don't modify value,
+    // as per [charconv.from.chars]/1.
+    //
+    // If LWG 3081 gets adopted, then we'll need to call to_float in this case too.
+    answer.ec = std::errc::result_out_of_range;
+    return answer;
+  }
+
   to_float(pns.negative, am, value);
   return answer;
 }
-- 
2.34.0


  parent reply	other threads:[~2021-11-16  0:25 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-16  0:25 [PATCH 1/5] libstdc++: Import the fast_float library Patrick Palka
2021-11-16  0:25 ` [PATCH 2/5] libstdc++: Apply modifications to our local copy of fast_float Patrick Palka
2021-11-19 21:47   ` Patrick Palka
2021-11-16  0:25 ` Patrick Palka [this message]
2021-11-19 21:49   ` [PATCH 3/5] libstdc++: Adjust fast_float's over/underflow behavior for conformnace Patrick Palka
2021-11-16  0:25 ` [PATCH 4/5] libstdc++: Use fast_float in std::from_chars for binary32/64 Patrick Palka
2021-11-16  0:25 ` [PATCH 5/5] libstdc++: Import MSVC floating-point std::from_chars testcases Patrick Palka
2021-11-16  7:59 ` [PATCH 1/5] libstdc++: Import the fast_float library Florian Weimer
2021-11-16  9:32   ` Jonathan Wakely
2021-11-16  9:46     ` Florian Weimer
2021-11-16 11:34       ` Jonathan Wakely
2021-11-16 15:30   ` Patrick Palka
2021-11-16 16:18     ` Daniel Krügler

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