Init

cppdraft/cfenv.md

@@ -0,0 +1,68 @@
+[cfenv]
+
+# 29 Numerics library [[numerics]](./#numerics)
+
+## 29.3 The floating-point environment [cfenv]
+
+### [29.3.1](#syn) Header <cfenv> synopsis [[cfenv.syn]](cfenv.syn)
+
+[🔗](#header:%3ccfenv%3e)
+
+#define FE_ALL_EXCEPT *see below*#define FE_DIVBYZERO *see below* // optional#define FE_INEXACT *see below* // optional#define FE_INVALID *see below* // optional#define FE_OVERFLOW *see below* // optional#define FE_UNDERFLOW *see below* // optional#define FE_DOWNWARD *see below* // optional#define FE_TONEAREST *see below* // optional#define FE_TOWARDZERO *see below* // optional#define FE_UPWARD *see below* // optional#define FE_DFL_ENV *see below*namespace std {// typesusing fenv_t = *object type*; using fexcept_t = *object type*; // functionsint feclearexcept(int except); int fegetexceptflag(fexcept_t* pflag, int except); int feraiseexcept(int except); int fesetexceptflag(const fexcept_t* pflag, int except); int fetestexcept(int except); int fegetround(); int fesetround(int mode); int fegetenv(fenv_t* penv); int feholdexcept(fenv_t* penv); int fesetenv(const fenv_t* penv); int feupdateenv(const fenv_t* penv);}
+
+[1](#syn-1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L138)
+
+The contents and meaning of the header [<cfenv>](#header:%3ccfenv%3e "29.3.1 Header <cfenv> synopsis [cfenv.syn]") are a subset of the C standard library header [<fenv.h>](support.c.headers.general#header:%3cfenv.h%3e "17.15.1 General [support.c.headers.general]") and
+only the declarations shown in the synopsis above are present[.](#syn-1.sentence-1)
+
+[*Note [1](#syn-note-1)*:
+
+This document does not require an implementation to support theFENV_ACCESS pragma;
+it is implementation-defined ([[cpp.pragma]](cpp.pragma "15.10 Pragma directive"))
+whether the pragma is supported[.](#syn-1.sentence-2)
+
+As a consequence,
+it is implementation-defined
+whether these functions can be used to test floating-point status flags,
+set floating-point control modes, or run under non-default mode settings[.](#syn-1.sentence-3)
+
+If the pragma is used to enable control over the floating-point environment,
+this document does not specify the effect on
+floating-point evaluation in constant expressions[.](#syn-1.sentence-4)
+
+— *end note*]
+
+See also: ISO/IEC 9899:2024, 7.6
+
+### [29.3.2](#thread) Threads [[cfenv.thread]](cfenv.thread)
+
+[1](#thread-1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L159)
+
+The floating-point environment has [thread storage duration](basic.stc.thread#def:storage_duration,thread "6.8.6.3 Thread storage duration [basic.stc.thread]")[.](#thread-1.sentence-1)
+
+The initial state for a thread's floating-point
+environment is the state of the floating-point environment of the thread that constructs
+the corresponding thread object ([[thread.thread.class]](thread.thread.class "32.4.3 Class thread"))
+or jthread object ([[thread.jthread.class]](thread.jthread.class "32.4.4 Class jthread"))
+at the time it
+constructed the object[.](#thread-1.sentence-2)
+
+[*Note [1](#thread-note-1)*:
+
+That is, the child thread gets the floating-point
+state of the parent thread at the time of the child's creation[.](#thread-1.sentence-3)
+
+— *end note*]
+
+[2](#thread-2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L172)
+
+A separate floating-point environment is maintained for each thread[.](#thread-2.sentence-1)
+
+Each function
+accesses the environment corresponding to its calling thread[.](#thread-2.sentence-2)