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Extra i386+gcc bn_div.c tune-up featuring inline division and saving

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the remainder left in %edx. Here is the resulting performance improvement
matrix (improvement as a result of this *and* previous tune-up committed
two days ago). The results were obtained by profiling the "div" part of
the crypto/bn/bnspeed.c.

CPU	BN_div	bn_div_words	overall	comment
------------------------------------------------------------------------
PII	+16%	accumulated by	+2-3%	PII multiplies damn fast! Taking
		inlining		multiplication out of the loop
					didn't make too much difference.
					Eliminating of the multiplication
					involved in remainder calculation
					is the major factor.

Pentium	+45%	accumulated by	+7-9%	mull isn't that fast and replacing
		inlining		multiplications with additions in
					the loop has more visible effect:-)

MIPS	+75%	+12%		+20-25%	In addition to the taking mults
R10000					out of the loop (giving 12% in the
					asm/mips3.s) three mults were
					eliminated in BN_div.

Alpha	+30%	+50%		+10-15%	Same as above. But remember that
EV4					bn_div_words is a C implementation.
					It takes 4 Alpha mults in C to do
					the same thing as 1 MIPS mult in
					assembler does. So the effect (50%)
					is more impressive. But not the
					overall one... Well, if Alpha
					bn_mul_add would be implemented
					in assembler overall improvement
					would be closer to MIPS...
This commit is contained in:
Andy Polyakov 1999-07-31 23:27:41 +00:00
parent 8d85b33eb5
commit 4c22909e31
1 changed files with 35 additions and 6 deletions
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41
crypto/bn/bn_div.c
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@ -204,15 +204,41 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
#ifdef BN_DIV3W
q=bn_div_3_words(wnump,d0,d1);
#else
BN_ULONG n0,n1,rem;
#if !defined(NO_ASM)
# if defined(__GNUC__) && __GNUC__>=2
# if defined(__i386)
/*
* There were two reasons for implementing this template:
* - GNU C generates a call to a function (__udivdi3 to be exact)
* in reply to ((((BN_ULLONG)n0)<<BN_BITS2)|n1)/d0 (I fail to
* understand why...);
* - divl doesn't only calculate quotient, but also leaves
* remainder in %edx which we can definitely use here:-)
*
* <appro@fy.chalmers.se>
*/
# define bn_div_words(n0,n1,d0) \
({ asm volatile ( \
"divl %4" \
: "=a"(q), "=d"(rem) \
: "a"(n1), "d"(n0), "g"(d0) \
: "cc"); \
q; \
})
# define REMINDER_IS_ALREADY_CALCULATED
# endif /* __<cpu> */
# endif /* __GNUC__ */
#endif /* NO_ASM */
BN_ULONG n0,n1,rem=0;
n0=wnump[0];
n1=wnump[-1];
if (n0 == d0)
q=BN_MASK2;
else
#if defined(BN_LLONG) && defined(BN_DIV2W)
q=((((BN_ULLONG)n0)<<BN_BITS2)|n1)/((BN_ULLONG)d0);
#if defined(BN_LLONG) && defined(BN_DIV2W) && !defined(bn_div_words)
q=((((BN_ULLONG)n0)<<BN_BITS2)|n1)/d0;
#else
q=bn_div_words(n0,n1,d0);
#endif
@ -220,13 +246,15 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
#ifdef BN_LLONG
BN_ULLONG t2;
#ifndef REMINDER_IS_ALREADY_CALCULATED
/*
* rem doesn't have to be BN_ULLONG. The least we
* know it's less that d0, isn't it?
*/
rem=(n1-q*d0)&BN_MASK2;
#endif
t2=(BN_ULLONG)d1*q;
for (;;)
{
if (t2 <= ((((BN_ULLONG)rem)<<BN_BITS2)|wnump[-2]))
@ -239,12 +267,13 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
#else
BN_ULONG t2l,t2h,ql,qh;
#ifndef REMINDER_IS_ALREADY_CALCULATED
/*
* It's more than enough with the only multiplication.
* See the comment above in BN_LLONG section...
*/
rem=(n1-q*d0)&BN_MASK2;
#endif
t2l=LBITS(d1); t2h=HBITS(d1);
ql =LBITS(q); qh =HBITS(q);
mul64(t2l,t2h,ql,qh); /* t2=(BN_ULLONG)d1*q; */
@ -261,7 +290,7 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
}
#endif
}
#endif /* BN_DIV3W */
#endif /* !BN_DIV3W */
wnum.d--; wnum.top++;
l0=bn_mul_words(tmp->d,sdiv->d,div_n,q);
tmp->d[div_n]=l0;