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Use 64-bit BignumInt wherever __uint128_t is available.

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gcc and clang both provide a type called __uint128_t when compiling
for 64-bit targets, code-generated more or less similarly to the way
64-bit long longs are handled on 32-bit targets (spanning two
registers, using ADD/ADC, that sort of thing). Where this is available
(and they also provide a handy macro to make it easy to detect), we
should obviously use it, so that we can handle bignums a larger chunk
at a time and make use of the full width of the hardware's multiplier.
Preliminary benchmarking using 'testbn' suggests a factor of about 2.5
improvement.

I've added the new possibility to the ifdefs in sshbn.h, and also
re-run contrib/make1305.py to generate a set of variants of the
poly1305 arithmetic for the new size of BignumInt.

(cherry picked from commit f8b27925ee)

Conflicts:
	sshccp.c

Cherry-picker's notes: the conflict arose because the original commit
also added new 64-bit autogenerated forms of dedicated Poly1305
arithmetic, which doesn't exist on this branch.
This commit is contained in:
Simon Tatham 2015-06-08 19:24:58 +01:00
parent 2725a51d3c
commit 445395c9d3
1 changed files with 18 additions and 1 deletions
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19
sshbn.h
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@ -20,7 +20,24 @@
* The C variant won't give the right answer, either.
*/
#if defined __GNUC__ && defined __i386__
#if defined __SIZEOF_INT128__
/* 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. If we have one of these, we can
* use a 64-bit BignumInt and a 128-bit BignumDblInt. */
typedef __uint64_t BignumInt;
typedef __uint128_t BignumDblInt;
#define BIGNUM_INT_MASK 0xFFFFFFFFFFFFFFFFULL
#define BIGNUM_TOP_BIT 0x8000000000000000ULL
#define BIGNUM_INT_BITS 64
#define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2)
#define DIVMOD_WORD(q, r, hi, lo, w) do { \
BignumDblInt n = (((BignumDblInt)hi) << BIGNUM_INT_BITS) | lo; \
q = n / w; \
r = n % w; \
} while (0)
#elif defined __GNUC__ && defined __i386__
typedef unsigned long BignumInt;
typedef unsigned long long BignumDblInt;
#define BIGNUM_INT_MASK 0xFFFFFFFFUL