From 779fc0a3e637fe8b339c04b7a79984a324edfcf8 Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@beefcake.parabola.nu>
Date: Sat, 11 Aug 2018 19:33:38 -0400
Subject: fastsum

---
 .gitignore                  |  1 +
 Makefile                    |  1 +
 go/src/cow-dedupe/dedupe.go |  2 +-
 src/fastsum.c               | 53 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 56 insertions(+), 1 deletion(-)
 create mode 100644 src/fastsum.c

diff --git a/.gitignore b/.gitignore
index 59a4ba5..0f4733c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 /cow-*
 *.o
+/fastsum
diff --git a/Makefile b/Makefile
index fe3d2ca..2d52dd6 100644
--- a/Makefile
+++ b/Makefile
@@ -11,6 +11,7 @@ CPPFLAGS += -O2 -D_FORTIFY_SOURCE=2
 all: cow-dedupe-range
 all: cow-extent-map
 all: cow-dedupe
+all: fastsum
 .PHONY: all
 
 %: src/%.o
diff --git a/go/src/cow-dedupe/dedupe.go b/go/src/cow-dedupe/dedupe.go
index 0c40d4a..42a0178 100644
--- a/go/src/cow-dedupe/dedupe.go
+++ b/go/src/cow-dedupe/dedupe.go
@@ -264,7 +264,7 @@ func main() {
 
 	sl = myStatusLine()
 	size2filenames := getChecksums(sl, "Getting sizes for files... %v/%v",
-		[]string{"stat", "--printf=%s  %n\\n", "--"}, spanningFiles)
+		[]string{"./fastsum"}, spanningFiles)
 	sl.End(true)
 
 	fmt.Fprintf(os.Stderr, " -> %d sets", len(size2filenames))
diff --git a/src/fastsum.c b/src/fastsum.c
new file mode 100644
index 0000000..4578ff2
--- /dev/null
+++ b/src/fastsum.c
@@ -0,0 +1,53 @@
+#include <errno.h>    /* for errno */
+#include <error.h>    /* for error(3gnu) */
+#include <fcntl.h>    /* for O_RDONLY */
+#include <inttypes.h> /* for PRI*, uint*_t, int*_t */
+#include <stdbool.h>  /* for bool */
+#include <stdio.h>    /* for printf */
+#include <sys/stat.h> /* for open(2), fstat(2) and struct stat */
+#include <unistd.h>   /* for close(2), read(2), lseek(2), SEEK_SET */
+
+int main(int argc, char *argv[]) {
+	bool err = false;
+	for (int i = 1; i < argc; i++) {
+		const char *filename = argv[i];
+
+		int fd = open(filename, O_RDONLY);
+		if (fd < 0) {
+			err = true;
+			error(0, errno, "open %s", filename);
+			continue;
+		}
+
+		struct stat st;
+		if (fstat(fd, &st) < 0) {
+			err = true;
+			error(0, errno, "fstat %s", filename);
+			close(fd);
+			continue;
+		}
+
+		if (lseek(fd, st.st_size/2, SEEK_SET) < 0) {
+			err = true;
+			error(0, errno, "lseek %s", filename);
+			close(fd);
+			continue;
+		}
+
+		uint8_t b;
+		int n = read(fd, &b, sizeof(b));
+		if (n <= 0) {
+			if (n == 0)
+				error(0, 0, "read %s: unexpected end of file", filename);
+			else
+				error(0, errno, "read %s", filename);
+			err = true;
+			close(fd);
+			continue;
+		}
+
+		printf("%"PRId64":%"PRIx8"  %s\n", (int64_t)st.st_size, b, filename);
+		close(fd);
+	}
+	return err ? 1 : 0;
+}
-- 
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