This is to make it easier for them to be selected individually depending
on the architecture instead of the other way around i.e. having each
architecture select a list of hacks up front. That makes for clearer
documentation as well.
Signed-off-by: Nicolas Pitre <nico@xxxxxxx>
---
block-sha1/sha1.c | 23 ++++++++++++++++++-----
1 files changed, 18 insertions(+), 5 deletions(-)
diff --git a/block-sha1/sha1.c b/block-sha1/sha1.c
index c3f1ae5..67c9bd0 100644
--- a/block-sha1/sha1.c
+++ b/block-sha1/sha1.c
@@ -11,10 +11,16 @@
#if defined(__i386__) || defined(__x86_64__)
+/*
+ * Force usage of rol or ror by selecting the one with the smaller constant.
+ * It _can_ generate slightly smaller code (a constant of 1 is special), but
+ * perhaps more importantly it's possibly faster on any uarch that does a
+ * rotate with a loop.
+ */
+
#define SHA_ASM(op, x, n) ({ unsigned int __res; __asm__(op " %1,%0":"=r" (__res):"i" (n), "0" (x)); __res; })
#define SHA_ROL(x,n) SHA_ASM("rol", x, n)
#define SHA_ROR(x,n) SHA_ASM("ror", x, n)
-#define SMALL_REGISTER_SET
#else
@@ -24,9 +30,6 @@
#endif
-/* This "rolls" over the 512-bit array */
-#define W(x) (array[(x)&15])
-
/*
* If you have 32 registers or more, the compiler can (and should)
* try to change the array[] accesses into registers. However, on
@@ -43,13 +46,23 @@
* Ben Herrenschmidt reports that on PPC, the C version comes close
* to the optimized asm with this (ie on PPC you don't want that
* 'volatile', since there are lots of registers).
+ *
+ * On ARM we get the best code generation by forcing a full memory barrier
+ * between each SHA_ROUND, otherwise gcc happily get wild with spilling and
+ * the stack frame size simply explode and performance goes down the drain.
*/
-#ifdef SMALL_REGISTER_SET
+
+#if defined(__i386__) || defined(__x86_64__)
#define setW(x, val) (*(volatile unsigned int *)&W(x) = (val))
+#elif defined(__arm__)
+ #define setW(x, val) do { W(x) = (val); __asm__("":::"memory"); } while (0)
#else
#define setW(x, val) (W(x) = (val))
#endif
+/* This "rolls" over the 512-bit array */
+#define W(x) (array[(x)&15])
+
/*
* Where do we get the source from? The first 16 iterations get it from
* the input data, the next mix it from the 512-bit array.
--
1.6.4.189.g282fa
--
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