+#include <openssl/rand.h>
+
+/* mod 128 saturating subtract of two 64-bit values in big-endian order */
+static int satsub64be(const unsigned char *v1,const unsigned char *v2)
+{ int ret,sat,brw,i;
+
+ if (sizeof(long) == 8) do
+ { const union { long one; char little; } is_endian = {1};
+ long l;
+
+ if (is_endian.little) break;
+ /* not reached on little-endians */
+ /* following test is redundant, because input is
+ * always aligned, but I take no chances... */
+ if (((size_t)v1|(size_t)v2)&0x7) break;
+
+ l = *((long *)v1);
+ l -= *((long *)v2);
+ if (l>128) return 128;
+ else if (l<-128) return -128;
+ else return (int)l;
+ } while (0);
+
+ ret = (int)v1[7]-(int)v2[7];
+ sat = 0;
+ brw = ret>>8; /* brw is either 0 or -1 */
+ if (ret & 0x80)
+ { for (i=6;i>=0;i--)
+ { brw += (int)v1[i]-(int)v2[i];
+ sat |= ~brw;
+ brw >>= 8;
+ }
+ }
+ else
+ { for (i=6;i>=0;i--)
+ { brw += (int)v1[i]-(int)v2[i];
+ sat |= brw;
+ brw >>= 8;
+ }
+ }
+ brw <<= 8; /* brw is either 0 or -256 */
+
+ if (sat&0xff) return brw | 0x80;
+ else return brw + (ret&0xFF);
+}