1 files changed, 170 insertions, 0 deletions
diff --git a/src/sequence/sequence.c b/src/sequence/sequence.c
new file mode 100644
index 0000000..852b05c
--- /dev/null
+++ b/src/sequence/sequence.c
@@ -0,0 +1,170 @@
+#include <stdlib.h>
+#include <string.h>
+
+#include "../core/index.h"
+
+#include "sequence.h"
+
+/*
+ * Bypass rendundant ZoO_START_OF_SEQUENCE_ID at the start of a sequence.
+ */
+/*@
+   requires
+   (
+      \valid(sequence+ (0 .. sequence_length))
+      || (sequence_length == 0)
+   );
+   requires \separated(sequence, sequence_offset);
+
+   assigns (*sequence_offset);
+
+   ensures (*sequence_offset < sequence_length);
+
+   ensures
+   (
+      (*sequence_offset == 0)
+      || (sequence[0 .. *sequence_offset] == ZoO_START_OF_SEQUENCE_ID)
+   );
+
+   ensures
+   (
+      (*sequence_offset == sequence_length)
+      || (sequence[*sequence_offset + 1] != ZoO_START_OF_SEQUENCE_ID)
+   );
+
+@*/
+static void bypass_redundant_sos
+(
+   const ZoO_index sequence [const restrict],
+   const size_t sequence_length,
+   size_t sequence_offset [const restrict static 1]
+)
+{
+   ZoO_index i;
+
+   *sequence_offset = 0;
+
+   /*@
+      loop invariant 0 <= i <= sequence_length;
+      loop invariant (*sequence_offset <= i);
+      loop invariant
+      (
+         (*sequence_offset == 0)
+         || (sequence[*sequence_offset] == ZoO_START_OF_SEQUENCE_ID)
+      );
+      loop invariant
+         (
+            (i == 0) || (sequence[0 .. (i - 1)] == ZoO_START_OF_SEQUENCE_ID)
+         );
+      loop assigns i, *sequence_offset;
+      loop variant (sequence_length - i);
+   @*/
+   for (i = 0; i < sequence_length; ++i)
+   {
+      if (sequence[i] != ZoO_START_OF_SEQUENCE_ID)
+      {
+         return;
+      }
+      else if (sequence[i] == ZoO_START_OF_SEQUENCE_ID)
+      {
+         *sequence_offset = i;
+      }
+   }
+}
+
+
+/* See "sequence.h" */
+/*@
+   \requires
+   (
+      \valid(sequence_a+ (0 .. sequence_a_length))
+      || (sequence_a_length == 0)
+   );
+
+   \requires
+   (
+      \valid(sequence_b+ (0 .. sequence_b_length))
+      || (sequence_b_length == 0)
+   );
+
+   assigns \result;
+@*/
+int ZoO_sequence_cmp
+(
+   const ZoO_index sequence_a [const],
+   size_t sequence_a_length,
+   const ZoO_index sequence_b [const],
+   size_t sequence_b_length
+)
+{
+   size_t min_length, a, b;
+   size_t a_offset, b_offset;
+   size_t i;
+   /*@ ghost size_t actual_a_length, actual_b_length; @*/
+
+   bypass_redundant_sos(sequence_a, sequence_a_length, &a_offset);
+   bypass_redundant_sos(sequence_b, sequence_b_length, &b_offset);
+
+   /*@ ghost actual_a_length = sequence_a_length; @*/
+   /*@ ghost actual_b_length = sequence_b_length; @*/
+
+   /*@ assert (a_offset <= sequence_a_length); @*/
+   sequence_a_length -= a_offset;
+   /*@ assert (b_offset <= sequence_b_length); @*/
+   sequence_b_length -= b_offset;
+
+   if (sequence_a_length < sequence_b_length)
+   {
+      min_length = sequence_a_length;
+   }
+   else
+   {
+      min_length = sequence_b_length;
+   }
+
+   /*@ assert (min_length <= sequence_a_length); @*/
+   /*@ assert (min_length <= sequence_b_length); @*/
+
+   /*@ assert (min_length + a_offset <= actual_a_length); @*/
+   /*@ assert (min_length + b_offset <= actual_b_length); @*/
+
+   /*@
+      loop invariant 0 <= i <= min_length;
+      loop assigns i;
+      loop variant (min_length - i);
+   @*/
+   for (i = 0; i < min_length; ++i)
+   {
+      /*@ assert ((i + a_offset) < actual_a_length); @*/
+      a = sequence_a[i + a_offset];
+      /*@ assert ((i + b_offset) < actual_b_length); @*/
+      b = sequence_b[i + b_offset];
+
+      if (a < b)
+      {
+         return -1;
+      }
+      else if (b > a)
+      {
+         return 1;
+      }
+      else if ((a == ZoO_END_OF_SEQUENCE_ID) && (b == ZoO_END_OF_SEQUENCE_ID))
+      {
+         return 0;
+      }
+   }
+
+   if (sequence_a_length > sequence_b_length)
+   {
+      return 1;
+   }
+   else if (sequence_a_length < sequence_b_length)
+   {
+      return -1;
+   }
+   else
+   {
+      return 0;
+   }
+}
+