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+/*
+ * math64.h provides the 64 bit unsigned integer add, multiply followed by modulo operation
+ * The linux/math64.h provides divide and multiply 64 bit integers but:
+ * 1. multiply: mul_u64_u64_shr - only returns 64 bits of the result and has to be called
+ * twice to get the complete 128 bits of the result.
+ * 2. Modulo operation of the result of addition and multiplication of u64 that may result
+ * in integers > 64 bits is not supported
+ * Hence this header to combine add/multiply followed by modulo of u64 integrers
+ * always resulting in u64.
+ *
+ * Copyright (c) 2016 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#ifndef include_vnet_math64_h
+#define include_vnet_math64_h
+#include <stdint.h>
+
+/*
+ * multiplies and returns result in hi and lo
+ */
+static inline void mul64by64(u64 a, u64 b, u64 * hi, u64 * lo)
+{
+ u64 a_lo = (u64) (uint32_t) a;
+ u64 a_hi = a >> 32;
+ u64 b_lo = (u64) (u32) b;
+ u64 b_hi = b >> 32;
+
+ u64 p0 = a_lo * b_lo;
+ u64 p1 = a_lo * b_hi;
+ u64 p2 = a_hi * b_lo;
+ u64 p3 = a_hi * b_hi;
+
+ u32 cy = (u32) (((p0 >> 32) + (u32) p1 + (u32) p2) >> 32);
+
+ *lo = p0 + (p1 << 32) + (p2 << 32);
+ *hi = p3 + (p1 >> 32) + (p2 >> 32) + cy;
+ return;
+}
+
+#define TWO64 18446744073709551616.0
+
+static inline u64 mod128by64(u64 x, u64 y, u64 m, double di)
+{
+ u64 q1, q2, q;
+ u64 p1, p0;
+ double dq;
+
+ /* calculate quotient first pass 53 bits */
+ dq = (TWO64 * (double)x + (double)y) * di;
+
+ if (dq >= TWO64)
+ q1 = 0xfffffffffffff800L;
+ else
+ q1 = dq;
+
+ /* q1 * m to compare the product to the dividend. */
+ mul64by64(q1, m, &p1, &p0);
+
+ /* Adjust quotient. is it > actual result: */
+ if (x < p1 || (x == p1 && y < p0))
+ {
+ /* q1 > quotient. calculate abs remainder */
+ x = p1 - (x + (p0 < y));
+ y = p0 - y;
+
+ /* use the remainder as new dividend to adjust quotient */
+ q2 = (u64) ((TWO64 * (double)x + (double)y) * di);
+ mul64by64(q2, m, &p1, &p0);
+
+ q = q1 - q2;
+ if (x < p1 || (x == p1 && y <= p0))
+ {
+ y = p0 - y;
+ }
+ else
+ {
+ y = p0 - y;
+ y += m;
+ q--;
+ }
+ }
+ else
+ {
+ x = x - (p1 + (y < p0));
+ y = y - p0;
+
+ q2 = (u64) ((TWO64 * (double)x + (double)y) * di);
+ mul64by64(q2, m, &p1, &p0);
+
+ q = q1 + q2;
+ if (x < p1 || (x == p1 && y < p0))
+ {
+ y = y - p0;
+ y += m;
+ q--;
+ }
+ else
+ {
+ y = y - p0;
+ if (y >= m)
+ {
+ y -= m;
+ q++;
+ }
+ }
+ }
+
+ return y;
+}
+
+/*
+ * returns a % p
+ */
+static inline u64 mod64by64(u64 a, u64 p, u64 primeinv)
+{
+ return (mod128by64(0, a, p, primeinv));
+}
+
+static inline void add64(u64 a, u64 b, u64 * whi, u64 * wlo)
+{
+ *wlo = a + b;
+ if (*wlo < a)
+ *whi = 1;
+
+}
+
+/*
+ * returns (a + b)%p
+ */
+static inline u64 add64_mod(u64 a, u64 b, u64 p, double pi)
+{
+ u64 shi = 0, slo = 0;
+
+ add64(a, b, &shi, &slo);
+ return (mod128by64(shi, slo, p, pi));
+}
+
+/*
+ * returns (ab) % p
+ */
+static inline u64 mul64_mod(u64 a, u64 b, u64 p, double pi)
+{
+ u64 phi = 0, plo = 0;
+
+ mul64by64(a, b, &phi, &plo);
+ return (mod128by64(phi, plo, p, pi));
+}
+
+#endif