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/* Copyright 2016 Brian Smith.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
#include "limbs.h"
#if defined(_MSC_VER)
#include <intrin.h>
/* MSVC 2015 RC, when compiling for x86 with /Ox (at least), miscompiles
* _addcarry_u32(c, 0, prod_hi, &x) like so:
*
* add eax,esi ; The previous add that might have set the carry flag.
* xor esi,esi ; OOPS! Carry flag is now reset!
* mov dword ptr [edi-4],eax
* adc esi,dword ptr [prod_hi]
*
* We test with MSVC 2015 update 2, so make sure we're using a version at least
* as new as that. */
#if _MSC_FULL_VER < 190023918
#error "MSVC 2015 Update 2 or later is required."
#endif
typedef uint8_t Carry;
#if LIMB_BITS == 64
#pragma intrinsic(_addcarry_u64, _subborrow_u64)
#define GFp_ADDCARRY_INTRINSIC _addcarry_u64
#define GFp_SUBBORROW_INTRINSIC _subborrow_u64
#elif LIMB_BITS == 32
#pragma intrinsic(_addcarry_u32, _subborrow_u32)
#define GFp_ADDCARRY_INTRINSIC _addcarry_u32
#define GFp_SUBBORROW_INTRINSIC _subborrow_u32
typedef uint64_t DoubleLimb;
#endif
#else
typedef Limb Carry;
#if LIMB_BITS == 64
typedef __uint128_t DoubleLimb;
#elif LIMB_BITS == 32
typedef uint64_t DoubleLimb;
#endif
#endif
/* |*r = a + b + carry_in|, returning carry out bit. |carry_in| must be 0 or 1.
*/
static inline Carry limb_adc(Limb *r, Limb a, Limb b, Carry carry_in) {
assert(carry_in == 0 || carry_in == 1);
Carry ret;
#if defined(GFp_ADDCARRY_INTRINSIC)
ret = GFp_ADDCARRY_INTRINSIC(carry_in, a, b, r);
#else
DoubleLimb x = (DoubleLimb)a + b + carry_in;
*r = (Limb)x;
ret = (Carry)(x >> LIMB_BITS);
#endif
assert(ret == 0 || ret == 1);
return ret;
}
/* |*r = a + b|, returning carry bit. */
static inline Carry limb_add(Limb *r, Limb a, Limb b) {
Carry ret;
#if defined(GFp_ADDCARRY_INTRINSIC)
ret = GFp_ADDCARRY_INTRINSIC(0, a, b, r);
#else
DoubleLimb x = (DoubleLimb)a + b;
*r = (Limb)x;
ret = (Carry)(x >> LIMB_BITS);
#endif
assert(ret == 0 || ret == 1);
return ret;
}
/* |*r = a - b - borrow_in|, returning the borrow out bit. |borrow_in| must be
* 0 or 1. */
static inline Carry limb_sbb(Limb *r, Limb a, Limb b, Carry borrow_in) {
assert(borrow_in == 0 || borrow_in == 1);
Carry ret;
#if defined(GFp_SUBBORROW_INTRINSIC)
ret = GFp_SUBBORROW_INTRINSIC(borrow_in, a, b, r);
#else
DoubleLimb x = (DoubleLimb)a - b - borrow_in;
*r = (Limb)x;
ret = (Carry)((x >> LIMB_BITS) & 1);
#endif
assert(ret == 0 || ret == 1);
return ret;
}
/* |*r = a - b|, returning borrow bit. */
static inline Carry limb_sub(Limb *r, Limb a, Limb b) {
Carry ret;
#if defined(GFp_SUBBORROW_INTRINSIC)
ret = GFp_SUBBORROW_INTRINSIC(0, a, b, r);
#else
DoubleLimb x = (DoubleLimb)a - b;
*r = (Limb)x;
ret = (Carry)((x >> LIMB_BITS) & 1);
#endif
assert(ret == 0 || ret == 1);
return ret;
}
static inline Carry limbs_add(Limb r[], const Limb a[], const Limb b[],
size_t num_limbs) {
assert(num_limbs >= 1);
Carry carry = limb_add(&r[0], a[0], b[0]);
for (size_t i = 1; i < num_limbs; ++i) {
carry = limb_adc(&r[i], a[i], b[i], carry);
}
return carry;
}
/* |r -= s|, returning the borrow. */
static inline Carry limbs_sub(Limb r[], const Limb a[], const Limb b[],
size_t num_limbs) {
assert(num_limbs >= 1);
Carry borrow = limb_sub(&r[0], a[0], b[0]);
for (size_t i = 1; i < num_limbs; ++i) {
borrow = limb_sbb(&r[i], a[i], b[i], borrow);
}
return borrow;
}
static inline void limbs_copy(Limb r[], const Limb a[], size_t num_limbs) {
for (size_t i = 0; i < num_limbs; ++i) {
r[i] = a[i];
}
}