From e802f9cc563abdb6f3ee4c4137edc6f293fdd8d2 Mon Sep 17 00:00:00 2001
From: Kyle Altendorf <sda@fstab.net>
Date: Tue, 10 Sep 2019 08:43:15 -0400
Subject: [PATCH] Make *c* and *d* rounds less intrusively configurable

---
 README.md     | 17 ++++++++++++-----
 halfsiphash.c |  8 ++++++--
 makefile      |  8 ++++++++
 siphash.c     |  8 ++++++--
 4 files changed, 32 insertions(+), 9 deletions(-)

diff --git a/README.md b/README.md
index 7af7657..1b4157b 100644
--- a/README.md
+++ b/README.md
@@ -42,13 +42,20 @@ verifies 64 test vectors, and
 does the same and prints intermediate values.
 
 The code can be adapted to implement SipHash-*c*-*d*, the version of SipHash
-with *c* compression rounds and *d* finalization rounds, by tweaking the
-lines
-```C
-#define cROUNDS 2
-#define dROUNDS 4
+with *c* compression rounds and *d* finalization rounds, by defining `cROUNDS`
+or `dROUNDS` when compiling.  This can be done with `-D` command line arguments
+to many compilers such as below.
+
+```sh
+gcc -Wall --std=c99 -DcROUNDS=2 -DdROUNDS=4 siphash.c halfsiphash.c test.c -o test
 ```
 
+The `makefile` also takes *c* and *d* rounds values as parameters.
+
+```sh
+make cROUNDS=2 dROUNDS=4
+``` 
+
 Obviously, if the number of rounds is modified then the test vectors
 won't verify.
 
diff --git a/halfsiphash.c b/halfsiphash.c
index 689e125..862de9d 100644
--- a/halfsiphash.c
+++ b/halfsiphash.c
@@ -19,8 +19,12 @@
 #include <string.h>
 
 /* default: SipHash-2-4 */
-#define cROUNDS 2
-#define dROUNDS 4
+#ifndef cROUNDS
+    #define cROUNDS 2
+#endif
+#ifndef dROUNDS
+    #define dROUNDS 4
+#endif
 
 #define ROTL(x, b) (uint32_t)(((x) << (b)) | ((x) >> (32 - (b))))
 
diff --git a/makefile b/makefile
index 8cf194a..eebe3e9 100644
--- a/makefile
+++ b/makefile
@@ -3,6 +3,14 @@ CFLAGS=-Wall --std=c99
 SRC=siphash.c halfsiphash.c test.c
 BIN=test debug vectors
 
+ifneq ($(cROUNDS),)
+CFLAGS:=$(CFLAGS) -DcROUNDS=$(cROUNDS)
+endif
+
+ifneq ($(dROUNDS),)
+CFLAGS:=$(CFLAGS) -DdROUNDS=$(dROUNDS)
+endif
+
 all:                    $(BIN)
 
 test:                   $(SRC)
diff --git a/siphash.c b/siphash.c
index 41c6f50..78bdf9f 100644
--- a/siphash.c
+++ b/siphash.c
@@ -20,8 +20,12 @@
 #include <string.h>
 
 /* default: SipHash-2-4 */
-#define cROUNDS 2
-#define dROUNDS 4
+#ifndef cROUNDS
+    #define cROUNDS 2
+#endif
+#ifndef dROUNDS
+    #define dROUNDS 4
+#endif
 
 #define ROTL(x, b) (uint64_t)(((x) << (b)) | ((x) >> (64 - (b))))