ip_checksum.c: Fixes for ip_csum_and_memcpy() alignment issues

Add explicit support for incremental operations which may be on
byte boundaries and misaligned. Since this is a memcpy() like function,
it needs to be robust in all byte operations.

Add code to perform the checksum 16 bits at a time when the destination
buffer pointer is not naturally aligned. The previous code did support
misaligned source data (via clib_mem_unaligned()), but didn't properly
align the destination pointer.

It would be possible to further optimize this by adding an optimzed
move operation where the source is aligned on natural boundaries.
Look at this as we optimize this function. At this point, I am
concentrating on correctness.

Change-Id: I2b0fd4795ec5c0ca294a733159c7355b54177690
Signed-off-by: Kevin Paul Herbert <kph@cisco.com>

1 files changed, 69 insertions, 35 deletions

diff --git a/vnet/vnet/ip/ip_checksum.c b/vnet/vnet/ip/ip_checksum.c
index 23e7889bc7e..680b7a44c63 100644
--- a/vnet/vnet/ip/ip_checksum.c
+++ b/vnet/vnet/ip/ip_checksum.c
@@ -109,76 +109,110 @@ do {									\
 ip_csum_t
 ip_csum_and_memcpy (ip_csum_t sum, void * dst, void * src, uword n_bytes)
 {
-  uword n_left, n_left_odd;
-  ip_csum_t * dst_even, * src_even;
+  uword n_left;
   ip_csum_t sum0 = sum, sum1;
-
-  dst_even = uword_to_pointer
-    (pointer_to_uword (dst) &~ (sizeof (sum) - 1),
-     ip_csum_t *);
-  src_even = src;
-
   n_left = n_bytes;
-  if ((n_left_odd = dst - (void *) dst_even))
-    {
-      u8 * d8 = dst, * s8 = src;
-      uword i, n_copy_odd;
 
-      n_copy_odd = clib_min (n_left, n_left_odd);
+  if (n_left && (pointer_to_uword (dst) & sizeof(u8)))
+    {
+      u8 * d8, val;
+
+      d8 = dst;
+      val = ((u8 *)src)[0];
+      d8[0] = val;
+      dst += 1;
+      src += 1;
+      n_left -= 1;
+      sum0 = ip_csum_with_carry (sum0, val << (8 * CLIB_ARCH_IS_LITTLE_ENDIAN));
+    }
 
-      for (i = 0; i < n_copy_odd; i++)
-	d8[i] = s8[i];
+  while ((n_left >= sizeof (u16)) && (pointer_to_uword (dst) & (sizeof (sum) - sizeof (u16))))
+    {
+      u16 * d16, * s16;
 
-      if (n_copy_odd != n_left_odd)
-	return sum0;
+      d16 = dst;
+      s16 = src;
+      
+      d16[0] = clib_mem_unaligned (&s16[0], u16);
 
-      sum0 = ip_csum_with_carry (sum0, dst_even[0]);
-      dst_even += 1;
-      src_even = (void *) (src + n_copy_odd);
-      n_left -= n_left_odd;
+      sum0 = ip_csum_with_carry (sum0, d16[0]);
+      dst += sizeof (u16);
+      src += sizeof (u16);
+      n_left -= sizeof (u16);
     }
 
   sum1 = 0;
-  while (n_left >= 2 * sizeof (dst_even[0]))
+  while (n_left >= 2 * sizeof (sum))
     {
       ip_csum_t dst0, dst1;
+      ip_csum_t *dst_even, *src_even;
 
+      dst_even = dst;
+      src_even = src;
       dst0 = clib_mem_unaligned (&src_even[0], ip_csum_t);
       dst1 = clib_mem_unaligned (&src_even[1], ip_csum_t);
 
       dst_even[0] = dst0;
       dst_even[1] = dst1;
 
-      dst_even += 2;
-      src_even += 2;
+      dst += 2 * sizeof(dst_even[0]);
+      src += 2 * sizeof(dst_even[0]);
       n_left -= 2 * sizeof (dst_even[0]);
 
       sum0 = ip_csum_with_carry (sum0, dst0);
       sum1 = ip_csum_with_carry (sum1, dst1);
     }
 
-  if (n_left >= 1 * sizeof (dst_even[0]))
+  sum0 = ip_csum_with_carry (sum0, sum1);
+  while (n_left >= 1 * sizeof (sum))
     {
-      ip_csum_t dst0;
+      ip_csum_t dst0, *dst_even, *src_even;
+
+      dst_even = dst;
+      src_even = src;
 
       dst0 = clib_mem_unaligned (&src_even[0], ip_csum_t);
 
       dst_even[0] = dst0;
 
-      dst_even += 1;
-      src_even += 1;
-      n_left -= 1 * sizeof (dst_even[0]);
+      dst += 1 * sizeof(sum);
+      src += 1 * sizeof(sum);
+      n_left -= 1 * sizeof (sum);
 
       sum0 = ip_csum_with_carry (sum0, dst0);
     }
 
-  if (n_left > 0)
+  while (n_left >= sizeof (u16))
     {
-      u8 * d8 = dst, * s8 = src;
-      uword i;
-      for (i = 0; i < n_left; i++)
-	d8[i] = s8[i];
+      u16 dst0, *dst_short, *src_short;
+
+      dst_short = dst;
+      src_short = src;
+
+      dst0 = clib_mem_unaligned (&src_short[0], u16);
+
+      dst_short[0] = dst0;
+
+      sum0 = ip_csum_with_carry (sum0, dst_short[0]);
+      dst += 1 * sizeof (dst0);
+      src += 1 * sizeof (dst0);
+      n_left -= 1 * sizeof (dst0);
+
+    }
+
+  if (n_left == 1)
+    {
+      u8 * d8, * s8, val;
+
+      d8 = dst;
+      s8 = src;
+
+      d8[0] = val = s8[0];
+      d8 += 1;
+      s8 += 1;
+      n_left -= 1;
+      sum0 = ip_csum_with_carry (sum0, val << (8 * CLIB_ARCH_IS_BIG_ENDIAN));
     }
 
-  return ip_csum_with_carry (sum0, sum1);
+  return sum0;
 }