diff --git "a/C/\346\227\240\346\225\214\347\246\273\350\260\261\344\275\215\350\277\220\347\256\227.md" "b/C/\346\227\240\346\225\214\347\246\273\350\260\261\344\275\215\350\277\220\347\256\227.md"
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@@ -0,0 +1,77 @@
+某科学的玩具操作系统中的一串用来映射到虚拟内存的代码:
+```c
+
+/* map page s (virtual) to d... okay, what am i doing? */
+
+void *__mapto(void *s, void *d, int attr) {
+#if CONFIG_64BIT
+	__archptr_t *lvl1, *lvl2, *lvl3, *p;
+	__archptr_t dest_addr;
+
+	dest_addr = (__archptr_t) d;
+	
+	lvl1 = (__archptr_t *) LVL1_PT[(dest_addr >> 39) & 4095];
+	
+	if (!lvl1) {
+		if (!(lvl1 = early_kmalloc(4096, 4096))) 
+			panic("mapto: Out of memory\n");
+
+		LVL1_PT[(dest_addr >> 39) & 4095] = (__archptr_t) lvl1 | DEFAULT_PAGE_ATTR;
+		memset(lvl1, 0, 4096);
+	}
+
+	p = (__archptr_t *) ((__archptr_t) lvl1 & ~0xfffu);
+	lvl2 = (__archptr_t *) p[(dest_addr >> 30) & 4095];
+
+	if (!lvl2) {
+		if (!(lvl2 = early_kmalloc(4096, 4096))) 
+			panic("mapto: Out of memory\n");
+
+		p[(dest_addr >> 30) & 4095] = (__archptr_t) lvl2 | DEFAULT_PAGE_ATTR;
+		memset(lvl2, 0, 4096);
+	}
+
+	lvl3 = (__archptr_t *) ((__archptr_t) lvl2 & ~0xfffu);
+
+	if (s) 
+		lvl3[(dest_addr >> 21) & 4095] = (__archptr_t) s | attr;
+
+	else 
+		lvl3[(dest_addr >> 21) & 4095] &= ~0xfffu | attr;
+
+	return d;
+#else
+
+	__archptr_t dest_addr = (__archptr_t) d;
+	__archptr_t *lvl1;
+	__archptr_t *lvl2;
+
+	dest_addr &= ~PAGE_MASK;
+	
+	/* 10 lvl1    10 lvl2    12 offset */
+	lvl1 = (__archptr_t *) LVL1_PT[dest_addr >> 22];
+
+	if (!lvl1) {
+		if (!(lvl1 = early_kmalloc(4096, 4096))) 
+			panic("mapto: Out of memory\n");
+
+		LVL1_PT[dest_addr >> 22] = (__archptr_t) lvl1 | DEFAULT_PAGE_ATTR;
+		memset(lvl1, 0, 4096);
+	}
+
+	lvl2 = (__archptr_t *) ((__archptr_t) lvl1 & ~0xffu);
+
+	if (!s) 
+		/* clear attributes and then set */
+
+		lvl2[(dest_addr >> 12) & 1023] &= ~0xff | attr;
+
+	else 
+		lvl2[(dest_addr >> 12) & 1023] = (__archptr_t) s | attr;
+
+
+	return (void *) dest_addr;
+#endif
+}
+
+```
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