1 files changed, 51 insertions, 0 deletions
diff --git a/CSAPP/tmul_asm.c b/CSAPP/tmul_asm.c
new file mode 100644
index 0000000..e496618
--- /dev/null
+++ b/CSAPP/tmul_asm.c
@@ -0,0 +1,51 @@
+int tmul_bug(long x, long y, long *dest)
+{
+	long result = 0;
+	*dest = x*y;
+	asm("setae %al");
+	return result;
+}
+
+int tmul_ok(long x, long y, long *dest)
+{
+	int result = 0;
+	*dest = x*y;
+	asm("setae %%bl		# Set low-order byte\n\t"
+	    "movzbl %%bl, %[val]	# Zero extend to be res"
+	    : [val] "=r" (result) /* Output */
+	    :			  /* No inputs */
+	    : "%bl"		  /* Overwrites */
+	    );
+	return result;
+}
+
+int tmul_ok2(long x, long y, long *dest)
+{
+	unsigned char result = 0;
+	*dest = x*y;
+
+	asm("setae %[b]		# Set result"
+	    : [b] "=r" (result) /* Output */
+	    );
+	return (int)result;
+}
+
+int umult_ok(unsigned long x, unsigned long y, unsigned long *dest)
+{
+	/*
+	 * GCC's asm choose the register to store asm operands
+	 * according to the type/size of the variable
+	 */
+	unsigned char result;
+
+	asm("movq %[x],%%rax	#Get x\n\t"
+	    "mulq %[y]	# Unsigned long mult x*y\n\t"
+	    "movq %%rax,%[p]	#Store low-order 8bytes at dest\n\t"
+	    "setae %[b]	#Set result"
+	    : [p] "=m" (*dest), [b] "=r" (result) /* Outputs */
+	    : [x] "r"  (x),	[y] "r"  (y)	  /* Inputs */
+	    : "%rax", "%rdx"			  /* Overwrites */
+	   );
+
+	return (int) result;
+}