Import official C23 code examples for Modern C (Jens Gustedt, 2024)HEADupstream-importmain

- Add official C source files, Makefile, c23-fallback.h, and LICENSE
- Update README.md with study mirror notice

1 files changed, 33 insertions, 0 deletions

diff --git a/crash.c b/crash.c
new file mode 100644
index 0000000..3a99d9e
--- /dev/null
+++ b/crash.c
@@ -0,0 +1,33 @@
+#include "c23-fallback.h"
+#include <stdio.h>
+#include <stdalign.h>
+#include <inttypes.h>
+#include <complex.h>
+#include "crash.h"
+
+void enable_alignment_check(void);
+typedef complex double cdbl;
+
+int main(void) {
+  enable_alignment_check();
+  /* An overlay of complex values and bytes. */
+  union {
+    cdbl val[2];
+    unsigned char buf[sizeof(cdbl[2])];
+  } toocomplex = {
+    .val = { 0.5 + 0.5*I, 0.75 + 0.75*I, },
+  };
+  printf("size/alignment: %zu/%zu\n",
+         sizeof(cdbl), alignof(cdbl));
+  /* Run over all offsets, and crash on misalignment. */
+  for (size_t offset = sizeof(cdbl); offset; offset /=2) {
+    printf("offset\t%zu:\t", offset);
+    fflush(stdout);
+    cdbl* bp = (cdbl*)(&toocomplex.buf[offset]); // align!
+    printf("%g\t+%gI\t", creal(*bp), cimag(*bp));
+    fflush(stdout);
+    *bp *= *bp;
+    printf("%g\t+%gI", creal(*bp), cimag(*bp));
+    fputc('\n', stdout);
+  }
+}