gosthash2012: Make `add512' to work in-place

[openssl-gost/engine.git] / gosthash2012.c

diff --git a/gosthash2012.c b/gosthash2012.c
index 201fe317ec23fb954e023c6b7a9fc48b5b0993eb..68ee0901875aaf782a3214ce4119eb631f2af44b 100644 (file)
--- a/gosthash2012.c
+++ b/gosthash2012.c
@@ -53,53 +53,48 @@ static INLINE void pad(gost2012_hash_ctx * CTX)
 
 }
 
-static INLINE void add512(const union uint512_u *x,
-                          const union uint512_u *y, union uint512_u *r)
+static INLINE void add512(union uint512_u * RESTRICT x,
+                          const union uint512_u * RESTRICT y)
 {
 #ifndef __GOST3411_BIG_ENDIAN__
-    unsigned int CF, OF;
-    unsigned long long tmp;
+    unsigned int CF;
     unsigned int i;
 
     CF = 0;
-    for (i = 0; i < 8; i++)
-    {
-        /* Detecting integer overflow condition for three numbers
-         * in a portable way is tricky a little. */
-
-        /* Step 1: numbers cause overflow */
-        tmp = x->QWORD[i] + y->QWORD[i];
-
-        /* Compare with any of two summands, no need to check both */
-        if (tmp < x->QWORD[i])
-            OF = 1;
-        else
-            OF = 0;
-
-        /* Step 2: carry bit causes overflow */
-        tmp += CF;
-
-        if (CF > 0 && tmp == 0)
-            OF = 1;
-
-        CF = OF;
-
-        r->QWORD[i] = tmp;
+    for (i = 0; i < 8; i++) {
+       const unsigned long long left = x->QWORD[i];
+       unsigned long long sum;
+
+       sum = left + y->QWORD[i] + CF;
+       /*
+        * (sum == left): is noop, because it's possible only
+        * when `left' is added with `0 + 0' or with `ULLONG_MAX + 1',
+        * in that case `CF' (carry) retain previous value, which is correct,
+        * because when `left + 0 + 0' there was no overflow (thus no carry),
+        * and when `left + ULLONG_MAX + 1' value is wrapped back to
+        * itself with overflow, thus creating carry.
+        *
+        * (sum != left):
+        * if `sum' is not wrapped (sum > left) there should not be carry,
+        * if `sum' is wrapped (sum < left) there should be carry.
+        */
+       if (sum != left)
+           CF = (sum < left);
+       x->QWORD[i] = sum;
     }
 #else
-    const unsigned char *xp, *yp;
-    unsigned char *rp;
+    const unsigned char *yp;
+    unsigned char *xp;
     unsigned int i;
     int buf;
 
-    xp = (const unsigned char *)&x[0];
+    xp = (unsigned char *)&x[0];
     yp = (const unsigned char *)&y[0];
-    rp = (unsigned char *)&r[0];
 
     buf = 0;
     for (i = 0; i < 64; i++) {
         buf = xp[i] + yp[i] + (buf >> 8);
-        rp[i] = (unsigned char)buf & 0xFF;
+        xp[i] = (unsigned char)buf & 0xFF;
     }
 #endif
 }
@@ -160,8 +155,8 @@ static INLINE void stage2(gost2012_hash_ctx * CTX, const unsigned char *data)
     memcpy(&m, data, sizeof(m));
     g(&(CTX->h), &(CTX->N), (const unsigned char *)&m);
 
-    add512(&(CTX->N), &buffer512, &(CTX->N));
-    add512(&(CTX->Sigma), &m, &(CTX->Sigma));
+    add512(&(CTX->N), &buffer512);
+    add512(&(CTX->Sigma), &m);
 }
 
 static INLINE void stage3(gost2012_hash_ctx * CTX)
@@ -183,9 +178,8 @@ static INLINE void stage3(gost2012_hash_ctx * CTX)
 
     g(&(CTX->h), &(CTX->N), (const unsigned char *)&(CTX->buffer));
 
-    add512(&(CTX->N), &buf, &(CTX->N));
-    add512(&(CTX->Sigma), (const union uint512_u *)&CTX->buffer[0],
-           &(CTX->Sigma));
+    add512(&(CTX->N), &buf);
+    add512(&(CTX->Sigma), (const union uint512_u *)&CTX->buffer[0]);
 
     g(&(CTX->h), &buffer0, (const unsigned char *)&(CTX->N));