mirror of
https://git.tartarus.org/simon/putty.git
synced 2025-01-10 01:48:00 +00:00
c2ec13c7e9
As I mentioned in the previous commit, I'm going to want PuTTY to be able to run sensibly when compiled with 64-bit Visual Studio, including handling bignums in 64-bit chunks for speed. Unfortunately, 64-bit VS does not provide any type we can use as BignumDblInt in that situation (unlike 64-bit gcc and clang, which give us __uint128_t). The only facilities it provides are compiler intrinsics to access an add-with-carry operation and a 64x64->128 multiplication (the latter delivering its product in two separate 64-bit output chunks). Hence, here's a substantial rework of the bignum code to make it implement everything in terms of _those_ primitives, rather than depending throughout on having BignumDblInt available to use ad-hoc. BignumDblInt does still exist, for the moment, but now it's an internal implementation detail of sshbn.h, only declared inside a new set of macros implementing arithmetic primitives, and not accessible to any code outside sshbn.h (which confirms that I really did catch all uses of it and remove them). The resulting code is surprisingly nice-looking, actually. You'd expect more hassle and roundabout circumlocutions when you drop down to using a more basic set of primitive operations, but actually, in many cases it's turned out shorter to write things in terms of the new BignumADC and BignumMUL macros - because almost all my uses of BignumDblInt were implementing those operations anyway, taking several lines at a time, and now they can do each thing in just one line. The biggest headache was Poly1305: I wasn't able to find any sensible way to adapt the existing Python script that generates the various per-int-size implementations of arithmetic mod 2^130-5, and so I had to rewrite it from scratch instead, with nothing in common with the old version beyond a handful of comments. But even that seems to have worked out nicely: the new version has much more legible descriptions of the high-level algorithms, by virtue of having a 'Multiprecision' type which wraps up the division into words, and yet Multiprecision's range analysis allows it to automatically drop out special cases such as multiplication by 5 being much easier than multiplication by another multi-word integer.
174 lines
7.2 KiB
C
174 lines
7.2 KiB
C
/*
|
|
* 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 __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 */
|