shaN: code shrink

function                                             old     new   delta
init512_lo                                            32      40      +8
init256                                               32      40      +8
sha256_begin                                          42      28     -14
sha512_begin                                          81      53     -28
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/2 up/down: 16/-42)            Total: -26 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/include/libbb.h b/include/libbb.h
index f406fc6..d05b2d4 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1514,7 +1514,7 @@
 
 typedef struct sha1_ctx_t {
 	uint32_t hash[8];    /* 5, +3 elements for sha256 */
-	uint64_t total64;
+	uint64_t total64;    /* must be directly after hash[] */
 	uint8_t wbuffer[64]; /* NB: always correctly aligned for uint64_t */
 	void (*process_block)(struct sha1_ctx_t*) FAST_FUNC;
 } sha1_ctx_t;
@@ -1527,7 +1527,7 @@
 #define sha256_end sha1_end
 typedef struct sha512_ctx_t {
 	uint64_t hash[8];
-	uint64_t total64[2];
+	uint64_t total64[2];  /* must be directly after hash[] */
 	uint8_t wbuffer[128]; /* NB: always correctly aligned for uint64_t */
 } sha512_ctx_t;
 void sha512_begin(sha512_ctx_t *ctx) FAST_FUNC;