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ppc64-mont.pl: commentary update.

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Andy Polyakov 2010-01-06 10:58:59 +00:00
parent dacdcf3c15
commit 1f23001d07
1 changed files with 17 additions and 16 deletions
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33
crypto/bn/asm/ppc64-mont.pl
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@ -47,22 +47,23 @@
# December 2009
# Adapted for 32-bit build this module delivers 25-120%, more for
# longer keys, performance improvement on 1.8GHz PPC970. However!
# This implementation utilizes even 64-bit integer operations and
# trouble is that most PPC operating systems don't preserve upper
# halves of general purpose registers upong signal delivery. They do
# preserve them upon context switch, but not signalling:-( This means
# that asynchronous signals have to be blocked upon entry to this
# subroutine. Signal masking (and complementary unmasking) has quite
# an impact on performance, naturally larger for shorter keys. It's
# so severe that 512-bit key performance can be as low as 1/3 of
# expected one. This is why this routine can be engaged for longer
# key operations only, see crypto/ppccap.c for further details.
# Alternative is to break dependence on upper halves on GPRs...
# MacOS X is an exception from this and doesn't require signal
# masking, and that's where above improvement coefficients were
# collected.
# Adapted for 32-bit build this module delivers 25-120%, yes, more
# than *twice* for longer keys, performance improvement over 32-bit
# ppc-mont.pl on 1.8GHz PPC970. However! This implementation utilizes
# even 64-bit integer operations and the trouble is that most PPC
# operating systems don't preserve upper halves of general purpose
# registers upon 32-bit signal delivery. They do preserve them upon
# context switch, but not signalling:-( This means that asynchronous
# signals have to be blocked upon entry to this subroutine. Signal
# masking (and of course complementary unmasking) has quite an impact
# on performance, naturally larger for shorter keys. It's so severe
# that 512-bit key performance can be as low as 1/3 of expected one.
# This is why this routine can be engaged for longer key operations
# only on these OSes, see crypto/ppccap.c for further details. MacOS X
# is an exception from this and doesn't require signal masking, and
# that's where above improvement coefficients were collected. For
# others alternative would be to break dependence on upper halves of
# GPRs by sticking to 32-bit integer operations...
$flavour = shift;