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sshbn.h
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sshbn.h
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/*
* sshbn.h: the assorted conditional definitions of BignumInt and
* multiply macros used throughout the bignum code to treat numbers as
* arrays of the most conveniently sized word for the target machine.
* Exported so that other code (e.g. poly1305) can use it too.
*
* This file must export, in whatever ifdef branch it ends up in:
*
* - two types: 'BignumInt' and 'BignumCarry'. BignumInt is an
* unsigned integer type which will be used as the base word size
* for all bignum operations. BignumCarry is an unsigned integer
* type used to hold the carry flag taken as input and output by
* the BignumADC macro (see below).
*
* - four constant macros: BIGNUM_INT_BITS, BIGNUM_INT_BYTES,
* BIGNUM_TOP_BIT, BIGNUM_INT_MASK. These should be more or less
* self-explanatory, but just in case, they give the number of bits
* in BignumInt, the number of bytes that works out to, the
* BignumInt value consisting of only the top bit, and the
* BignumInt value with all bits set.
*
* - four statement macros: BignumADC, BignumMUL, BignumMULADD,
* BignumMULADD2. These do various kinds of multi-word arithmetic,
* and all produce two output values.
* * BignumADC(ret,retc,a,b,c) takes input BignumInt values a,b
* and a BignumCarry c, and outputs a BignumInt ret = a+b+c and
* a BignumCarry retc which is the carry off the top of that
* addition.
* * BignumMUL(rh,rl,a,b) returns the two halves of the
* double-width product a*b.
* * BignumMULADD(rh,rl,a,b,addend) returns the two halves of the
* double-width value a*b + addend.
* * BignumMULADD2(rh,rl,a,b,addend1,addend2) returns the two
* halves of the double-width value a*b + addend1 + addend2.
*
* Every branch of the main ifdef below defines the type BignumInt and
* the value BIGNUM_INT_BITS. The other three constant macros are
* filled in by common code further down.
*
* Most branches also define a macro DEFINE_BIGNUMDBLINT containing a
* typedef statement which declares a type _twice_ the length of a
* BignumInt. This causes the common code further down to produce a
* default implementation of the four statement macros in terms of
* that double-width type, and also to defined BignumCarry to be
* BignumInt.
*
* However, if a particular compile target does not have a type twice
* the length of the BignumInt you want to use but it does provide
* some alternative means of doing add-with-carry and double-word
* multiply, then the ifdef branch in question can just define
* BignumCarry and the four statement macros itself, and that's fine
* too.
*/
#if defined __SIZEOF_INT128__
/*
* 64-bit BignumInt using gcc/clang style 128-bit BignumDblInt.
*
* gcc and clang both provide a __uint128_t type on 64-bit targets
* (and, when they do, indicate its presence by the above macro),
* using the same 'two machine registers' kind of code generation
* that 32-bit targets use for 64-bit ints.
*/
typedef unsigned long long BignumInt;
#define BIGNUM_INT_BITS 64
#define DEFINE_BIGNUMDBLINT typedef __uint128_t BignumDblInt
#elif defined _MSC_VER && defined _M_AMD64
/*
* 64-bit BignumInt, using Visual Studio x86-64 compiler intrinsics.
*
* 64-bit Visual Studio doesn't provide very much in the way of help
* here: there's no int128 type, and also no inline assembler giving
* us direct access to the x86-64 MUL or ADC instructions. However,
* there are compiler intrinsics giving us that access, so we can
* use those - though it turns out we have to be a little careful,
* since they seem to generate wrong code if their pointer-typed
* output parameters alias their inputs. Hence all the internal temp
* variables inside the macros.
*/
#include <intrin.h>
typedef unsigned char BignumCarry; /* the type _addcarry_u64 likes to use */
typedef unsigned __int64 BignumInt;
#define BIGNUM_INT_BITS 64
#define BignumADC(ret, retc, a, b, c) \
do { \
BignumInt ADC_tmp; \
(retc) = _addcarry_u64(c, a, b, &ADC_tmp); \
(ret) = ADC_tmp; \
} while (0)
#define BignumMUL(rh, rl, a, b) \
do { \
BignumInt MULADD_hi; \
(rl) = _umul128(a, b, &MULADD_hi); \
(rh) = MULADD_hi; \
} while (0)
#define BignumMULADD(rh, rl, a, b, addend) \
do { \
BignumInt MULADD_lo, MULADD_hi; \
MULADD_lo = _umul128(a, b, &MULADD_hi); \
MULADD_hi += _addcarry_u64(0, MULADD_lo, (addend), &(rl)); \
(rh) = MULADD_hi; \
} while (0)
#define BignumMULADD2(rh, rl, a, b, addend1, addend2) \
do { \
BignumInt MULADD_lo1, MULADD_lo2, MULADD_hi; \
MULADD_lo1 = _umul128(a, b, &MULADD_hi); \
MULADD_hi += _addcarry_u64(0, MULADD_lo1, (addend1), &MULADD_lo2); \
MULADD_hi += _addcarry_u64(0, MULADD_lo2, (addend2), &(rl)); \
(rh) = MULADD_hi; \
} while (0)
#elif defined __GNUC__ || defined _LLP64 || __STDC__ >= 199901L
/* 32-bit BignumInt, using C99 unsigned long long as BignumDblInt */
typedef unsigned int BignumInt;
#define BIGNUM_INT_BITS 32
#define DEFINE_BIGNUMDBLINT typedef unsigned long long BignumDblInt
#elif defined _MSC_VER && defined _M_IX86
/* 32-bit BignumInt, using Visual Studio __int64 as BignumDblInt */
typedef unsigned int BignumInt;
#define BIGNUM_INT_BITS 32
#define DEFINE_BIGNUMDBLINT typedef unsigned __int64 BignumDblInt
#elif defined _LP64
/*
* 32-bit BignumInt, using unsigned long itself as BignumDblInt.
*
* Only for platforms where long is 64 bits, of course.
*/
typedef unsigned int BignumInt;
#define BIGNUM_INT_BITS 32
#define DEFINE_BIGNUMDBLINT typedef unsigned long BignumDblInt
#else
/*
* 16-bit BignumInt, using unsigned long as BignumDblInt.
*
* This is the final fallback for real emergencies: C89 guarantees
* unsigned short/long to be at least the required sizes, so this
* should work on any C implementation at all. But it'll be
* noticeably slow, so if you find yourself in this case you
* probably want to move heaven and earth to find an alternative!
*/
typedef unsigned short BignumInt;
#define BIGNUM_INT_BITS 16
#define DEFINE_BIGNUMDBLINT typedef unsigned long BignumDblInt
#endif
/*
* Common code across all branches of that ifdef: define the three
* easy constant macros in terms of BIGNUM_INT_BITS.
*/
#define BIGNUM_INT_BYTES (BIGNUM_INT_BITS / 8)
#define BIGNUM_TOP_BIT (((BignumInt)1) << (BIGNUM_INT_BITS - 1))
#define BIGNUM_INT_MASK (BIGNUM_TOP_BIT | (BIGNUM_TOP_BIT - 1))
/*
* Common code across _most_ branches of the ifdef: define a set of
* statement macros in terms of the BignumDblInt type provided. In
* this case, we also define BignumCarry to be the same thing as
* BignumInt, for simplicity.
*/
#ifdef DEFINE_BIGNUMDBLINT
typedef BignumInt BignumCarry;
#define BignumADC(ret, retc, a, b, c) \
do { \
DEFINE_BIGNUMDBLINT; \
BignumDblInt ADC_temp = (BignumInt)(a); \
ADC_temp += (BignumInt)(b); \
ADC_temp += (c); \
(ret) = (BignumInt)ADC_temp; \
(retc) = (BignumCarry)(ADC_temp >> BIGNUM_INT_BITS); \
} while (0)
#define BignumMUL(rh, rl, a, b) \
do { \
DEFINE_BIGNUMDBLINT; \
BignumDblInt MUL_temp = (BignumInt)(a); \
MUL_temp *= (BignumInt)(b); \
(rh) = (BignumInt)(MUL_temp >> BIGNUM_INT_BITS); \
(rl) = (BignumInt)(MUL_temp); \
} while (0)
#define BignumMULADD(rh, rl, a, b, addend) \
do { \
DEFINE_BIGNUMDBLINT; \
BignumDblInt MUL_temp = (BignumInt)(a); \
MUL_temp *= (BignumInt)(b); \
MUL_temp += (BignumInt)(addend); \
(rh) = (BignumInt)(MUL_temp >> BIGNUM_INT_BITS); \
(rl) = (BignumInt)(MUL_temp); \
} while (0)
#define BignumMULADD2(rh, rl, a, b, addend1, addend2) \
do { \
DEFINE_BIGNUMDBLINT; \
BignumDblInt MUL_temp = (BignumInt)(a); \
MUL_temp *= (BignumInt)(b); \
MUL_temp += (BignumInt)(addend1); \
MUL_temp += (BignumInt)(addend2); \
(rh) = (BignumInt)(MUL_temp >> BIGNUM_INT_BITS); \
(rl) = (BignumInt)(MUL_temp); \
} while (0)
#endif /* DEFINE_BIGNUMDBLINT */