From 56a5616401d150cb39d4133c4a149c0fbc744c82 Mon Sep 17 00:00:00 2001
From: Antonio Ospite <ospite@studenti.unina.it>
Date: Fri, 8 Nov 2013 17:31:04 +0100
Subject: [PATCH] Add an example about summing an array of integers

---
 Makefile               | 12 +++++---
 inline-asm-array-sum.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 84 insertions(+), 4 deletions(-)
 create mode 100644 inline-asm-array-sum.c

diff --git a/Makefile b/Makefile
index 1e601a4..b350291 100644
--- a/Makefile
+++ b/Makefile
@@ -29,11 +29,15 @@ ifneq ($(CC),clang)
   CFLAGS += -Wunsafe-loop-optimizations
 endif
 
+EXECUTABLES := inline-asm-sum inline-asm-array-sum
 
-inline-asm-sum: inline-asm-sum.o
+all: $(EXECUTABLES)
 
 clean:
-	rm -f *~ *.o inline-asm-sum
+	rm -f *~ *.o $(EXECUTABLES)
 
-test: inline-asm-sum
-	valgrind --leak-check=full --show-reachable=yes ./inline-asm-sum
+test: $(EXECUTABLES)
+	@for executable in $?; \
+	do \
+	  valgrind --leak-check=full --show-reachable=yes ./$$executable; \
+	done
diff --git a/inline-asm-array-sum.c b/inline-asm-array-sum.c
new file mode 100644
index 0000000..7eb7ae8
--- /dev/null
+++ b/inline-asm-array-sum.c
@@ -0,0 +1,76 @@
+/*
+ * inline-asm-array-sum - an example of inline assembly accessing arrays
+ *
+ * Copyright (C) 2013  Antonio Ospite <ospite@studenti.unina.it>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+#define SIZE 10000001
+
+static int array_sum(int *values, unsigned int n)
+{
+	int sum = 0;
+
+#if defined(__x86_64__)
+	__asm__(
+		"movq $0, %%rdi\n\t" /* i = 0 */
+		".REPEAT:\n\t"
+		"cmpl %%edi, %%ecx\n\t" /* if (i == n) */
+		"je .DONE\n\t"
+		/* TODO: try incrementing the pointer by 4 */
+		"movq (%%rbx,%%rdi,4), %%rdx\n\t" /* tmp = values[i]; 64 bit register */
+		"addl %%edx, %%eax\n\t" /* sum += tmp[31:0]; */
+		"incl %%edi\n\t" /* i++ */
+		"jmp .REPEAT\n\t"
+		".DONE:\n\t"
+		: "=a"(sum)
+		: "b"(values), "c"(n), "0"(sum)
+		: "%rdx", "%rdi", "cc"
+		);
+#else
+	unsigned int i;
+	for (i = 0; i < n; i++)
+		sum += values[i];
+#endif
+	return sum;
+}
+
+int main(void)
+{
+	int *values;
+	int i;
+	int sum;
+	int expected;
+	int n = SIZE;
+
+	srand(time(0));
+
+	values = malloc(n * sizeof(*values));
+
+	expected = 0;
+	for (i = 0; i < n; i++) {
+		values[i] = rand();
+		expected += values[i];
+	}
+
+	sum = array_sum(values, n);
+
+	printf("expected = %d; sum = %d; %s\n", expected, sum, sum == expected ? "OK" : "FAILED");
+	return (sum == expected);
+}
-- 
2.1.4