user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/tests/ansi/ungetc.c

@@ -0,0 +1,76 @@
+#include <stdio.h>
+#include <assert.h>
+
+#ifdef USE_HOST_LIBC
+#define TEST_FILE "ungetc-host-libc.tmp"
+#else
+#define TEST_FILE "ungetc.tmp"
+#endif
+
+void test(int buffering) {
+	FILE *f = fopen(TEST_FILE, "w");
+	for(int c = '0'; c <= '9'; c++) {
+		fputc(c, f);
+	}
+	fclose(f);
+
+	f = fopen(TEST_FILE, "r");
+	if (!buffering) {
+		setbuf(f, NULL);
+	}
+
+	assert(ungetc('x', f) == 'x');
+	assert(fgetc(f) == 'x');
+
+	// Test pushing back the same character
+	for (int c = '0'; c <= '9'; c++) {
+		assert(fgetc(f) == c);
+		assert(ungetc(c, f) == c);
+		assert(fgetc(f) == c);
+	}
+	assert(fgetc(f) == EOF);
+	assert(ungetc(EOF, f) == EOF);
+
+	// Even though the spec does not guarantee it, we should be able to
+	// ungetc more than one character.
+	assert(ungetc('x', f) == 'x');
+	assert(ungetc('y', f) == 'y');
+	assert(fgetc(f) == 'y');
+	assert(fgetc(f) == 'x');
+
+	// Seeking should discard the effects of ungetc.
+	assert(ungetc('x', f) == 'x');
+	rewind(f);
+
+	// Test pushing back a different character
+	for (int c = '0'; c <= '9'; c++) {
+		assert(fgetc(f) == c);
+		assert(ungetc(c - '0' + 'a', f) == c - '0' + 'a');
+		assert(fgetc(f) == c - '0' + 'a');
+	}
+
+#ifndef USE_HOST_LIBC
+	// Too many ungetcs should fail.
+	int eof = 0;
+	for (int i = 0; i < 100; i++) {
+		if (ungetc('x', f) == EOF) {
+			eof = 1;
+			break;
+		}
+	}
+	assert(eof);
+#endif
+
+	fclose(f);
+
+	// TODO: Test with other operations, like fread.
+}
+
+int main() {
+	fprintf(stderr, "with buffering...\n");
+	test(1);
+	fprintf(stderr, "without buffering...\n");
+	test(0);
+
+	return 0;
+}