From b3e9e62599532050fc776c5e8f076915b56c2235 Mon Sep 17 00:00:00 2001
From: David Faulkner <d@davo.co>
Date: Fri, 7 Aug 2026 23:40:47 -0500
Subject: Import official C23 code examples for Modern C (Jens Gustedt, 2024)

- Add official C source files, Makefile, c23-fallback.h, and LICENSE
- Update README.md with study mirror notice
---
 fp_except.c | 88 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 fp_except.c

(limited to 'fp_except.c')

diff --git a/fp_except.c b/fp_except.c
new file mode 100644
index 0000000..5dc63ec
--- /dev/null
+++ b/fp_except.c
@@ -0,0 +1,88 @@
+#include "c23-fallback.h"
+#include <stdio.h>
+#include <fenv.h>
+#include <float.h>
+#ifndef INFINITY
+#include <math.h>
+#endif
+
+#if !defined(__STDC_IEC_559__) && !defined(__STDC_IEC_60559_BFP__) && !FE_ALL_EXCEPT
+#error "floating-point arithmetic is too weird"
+#endif
+
+static_assert(FE_ALL_EXCEPT, "floating point exceptions are not supported");
+
+#ifdef FENV_OFF
+#warning "switching FENV_ACCESS off"
+#pragma STDC FENV_ACCESS OFF
+#else
+#pragma STDC FENV_ACCESS ON
+#endif
+
+bool const has_inf =
+#ifdef INFINITY
+  (1.0/0.0 == INFINITY)
+#else
+  false
+#endif
+  ;
+
+int excepts[] = {
+#ifdef FE_DIVBYZERO
+  FE_DIVBYZERO,
+#endif
+#ifdef FE_INEXACT
+  FE_INEXACT,
+#endif
+#ifdef FE_INVALID
+  FE_INVALID,
+#endif
+#ifdef FE_OVERFLOW
+  FE_OVERFLOW,
+#endif
+#ifdef FE_UNDERFLOW
+  FE_UNDERFLOW,
+#endif
+};
+
+void printexcept(void) {
+  char const* name[] = {
+#ifdef FE_DIVBYZERO
+    "divbyzero",
+#endif
+#ifdef FE_INEXACT
+    "inexact",
+#endif
+#ifdef FE_INVALID
+    "invalid",
+#endif
+#ifdef FE_OVERFLOW
+    "overflow",
+#endif
+#ifdef FE_UNDERFLOW
+    "underflow",
+#endif
+  };
+  int except = fetestexcept(FE_ALL_EXCEPT);
+  if (except) {
+    printf("[");
+    for (unsigned j = 0; except; except &= ~excepts[j], ++j)
+      if (excepts[j] & except)
+        printf("%s ", name[j]);
+    printf("]");
+  }
+}
+
+int main (int argc, char* argv[static argc+1]) {
+  printf("division by zero is %sequal to INFINITY\n", has_inf ? "" : "un");
+  for (unsigned i = 1; i < argc; i++) {
+    feclearexcept(FE_ALL_EXCEPT);
+    double x = strtod(argv[i], nullptr);
+    printf("%g ", x);
+    printexcept();
+    feclearexcept(FE_ALL_EXCEPT);
+    printf(": %g ", 1.0/x);
+    printexcept();
+    puts("");
+  }
+}
-- 
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