1 files changed, 48 insertions, 0 deletions
diff --git a/src/wincrt.c b/src/wincrt.c
new file mode 100644
index 0000000..8ffa6cb
--- /dev/null
+++ b/src/wincrt.c
@@ -0,0 +1,48 @@
+/* This file is dedicated to the public domain. */
+
+// We get most of the libc functions from ucrtbase.dll, which comes with
+// Windows, but for some reason a few of the intrinsic-y things are part of
+// vcruntime, which does *not* come with Windows!!! We can statically link just
+// that part but it adds ~12KiB of random useless bloat to our binary. So, let's
+// just implement the handful of required things here instead. This is only for
+// release/non-debug builds; we want the extra checks in Microsoft's CRT when
+// debugging.
+//
+// Is it actually reasonable to have to do any of this? Of course not.
+
+// TODO(opt): this feels like a sad implementation, can we do marginally better?
+int memcmp(const void *x_, const void *y_, unsigned int sz) {
+	const char *x = x_, *y = y_;
+	for (unsigned int i = 0; i < sz; ++i) {
+		if (x[i] > y[i]) return 1;
+		if (x[i] < y[i]) return -1;
+	}
+	return 0;
+}
+
+void *memcpy(void *restrict x, const void *restrict y, unsigned int sz) {
+#ifdef __clang__
+	__asm__ volatile (
+		"rep movsb\n" :
+		"=D" (x), "=S" (y), "=c" (sz) :
+		"0" (x), "1" (y), "2" (sz) :
+		"memory"
+	);
+#else // terrible fallback just in case someone wants to use this with MSVC
+	char *restrict xb = x; const char *restrict yb = y;
+	for (unsigned int i = 0; i < sz; ++i) xb[i] = yb[i];
+#endif
+	return x;
+}
+
+int __stdcall _DllMainCRTStartup(void *inst, unsigned int reason,
+		void *reserved) {
+	return 1;
+}
+
+#ifdef __clang__
+__attribute__((used))
+#endif
+int _fltused = 1;
+
+// vi: sw=4 ts=4 noet tw=80 cc=80