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Merge bitcoin#596: Make WINDOW_G configurable
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a61a93f Clean up ./configure help strings (Tim Ruffing)
2842dc5 Make WINDOW_G configurable (Tim Ruffing)

Pull request description:

  This makes WINDOW_G a configurable value in the range of [2..24].
  The upper limit of 24 is a defensive choice. The code is probably
  correct for values up to 33 but those larger values yield in huge
  tables (>= 256MiB), which are i) unlikely to be really beneficial
  in practice and ii) increasingly difficult to test.

  The main point of this is not to make the window size configurable (using ./configure) but rather to use an external #define for the window size, which makes it configurable for embedded system that rely on their own build system (like in bitcoin#595).

ACKs for commit a61a93:

Tree-SHA512: 0d58fdf4763340ddab992e95f6302a33d891476a7ac1748202ee99808e72b20754bb6935cbeaf0bb36077abaaff7d65f4848b1af64f1a0a5258239ba0d27020c
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@gmaxwell
gmaxwell committed May 25, 2019
2 parents 1a02d6c + a61a93f commit 36698dc
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Showing 3 changed files with 85 additions and 28 deletions.
62 changes: 47 additions & 15 deletions configure.ac
View file
Original file line number Diff line number Diff line change
Expand Up @@ -85,42 +85,42 @@ AC_COMPILE_IFELSE([AC_LANG_SOURCE([[char foo;]])],
])

AC_ARG_ENABLE(benchmark,
AS_HELP_STRING([--enable-benchmark],[compile benchmark (default is yes)]),
AS_HELP_STRING([--enable-benchmark],[compile benchmark [default=yes]]),
[use_benchmark=$enableval],
[use_benchmark=yes])

AC_ARG_ENABLE(coverage,
AS_HELP_STRING([--enable-coverage],[enable compiler flags to support kcov coverage analysis]),
AS_HELP_STRING([--enable-coverage],[enable compiler flags to support kcov coverage analysis [default=no]]),
[enable_coverage=$enableval],
[enable_coverage=no])

AC_ARG_ENABLE(tests,
AS_HELP_STRING([--enable-tests],[compile tests (default is yes)]),
AS_HELP_STRING([--enable-tests],[compile tests [default=yes]]),
[use_tests=$enableval],
[use_tests=yes])

AC_ARG_ENABLE(openssl_tests,
AS_HELP_STRING([--enable-openssl-tests],[enable OpenSSL tests, if OpenSSL is available (default is auto)]),
AS_HELP_STRING([--enable-openssl-tests],[enable OpenSSL tests [default=auto]]),
[enable_openssl_tests=$enableval],
[enable_openssl_tests=auto])

AC_ARG_ENABLE(experimental,
AS_HELP_STRING([--enable-experimental],[allow experimental configure options (default is no)]),
AS_HELP_STRING([--enable-experimental],[allow experimental configure options [default=no]]),
[use_experimental=$enableval],
[use_experimental=no])

AC_ARG_ENABLE(exhaustive_tests,
AS_HELP_STRING([--enable-exhaustive-tests],[compile exhaustive tests (default is yes)]),
AS_HELP_STRING([--enable-exhaustive-tests],[compile exhaustive tests [default=yes]]),
[use_exhaustive_tests=$enableval],
[use_exhaustive_tests=yes])

AC_ARG_ENABLE(endomorphism,
AS_HELP_STRING([--enable-endomorphism],[enable endomorphism (default is no)]),
AS_HELP_STRING([--enable-endomorphism],[enable endomorphism [default=no]]),
[use_endomorphism=$enableval],
[use_endomorphism=no])

AC_ARG_ENABLE(ecmult_static_precomputation,
AS_HELP_STRING([--enable-ecmult-static-precomputation],[enable precomputed ecmult table for signing (default is yes)]),
AS_HELP_STRING([--enable-ecmult-static-precomputation],[enable precomputed ecmult table for signing [default=auto]]),
[use_ecmult_static_precomputation=$enableval],
[use_ecmult_static_precomputation=auto])

Expand All @@ -130,26 +130,35 @@ AC_ARG_ENABLE(module_ecdh,
[enable_module_ecdh=no])

AC_ARG_ENABLE(module_recovery,
AS_HELP_STRING([--enable-module-recovery],[enable ECDSA pubkey recovery module (default is no)]),
AS_HELP_STRING([--enable-module-recovery],[enable ECDSA pubkey recovery module [default=no]]),
[enable_module_recovery=$enableval],
[enable_module_recovery=no])

AC_ARG_ENABLE(jni,
AS_HELP_STRING([--enable-jni],[enable libsecp256k1_jni (default is no)]),
AS_HELP_STRING([--enable-jni],[enable libsecp256k1_jni [default=no]]),
[use_jni=$enableval],
[use_jni=no])

AC_ARG_WITH([field], [AS_HELP_STRING([--with-field=64bit|32bit|auto],
[Specify Field Implementation. Default is auto])],[req_field=$withval], [req_field=auto])
[finite field implementation to use [default=auto]])],[req_field=$withval], [req_field=auto])

AC_ARG_WITH([bignum], [AS_HELP_STRING([--with-bignum=gmp|no|auto],
[Specify Bignum Implementation. Default is auto])],[req_bignum=$withval], [req_bignum=auto])
[bignum implementation to use [default=auto]])],[req_bignum=$withval], [req_bignum=auto])

AC_ARG_WITH([scalar], [AS_HELP_STRING([--with-scalar=64bit|32bit|auto],
[Specify scalar implementation. Default is auto])],[req_scalar=$withval], [req_scalar=auto])
[scalar implementation to use [default=auto]])],[req_scalar=$withval], [req_scalar=auto])

AC_ARG_WITH([asm], [AS_HELP_STRING([--with-asm=x86_64|arm|no|auto]
[Specify assembly optimizations to use. Default is auto (experimental: arm)])],[req_asm=$withval], [req_asm=auto])
AC_ARG_WITH([asm], [AS_HELP_STRING([--with-asm=x86_64|arm|no|auto],
[assembly optimizations to use (experimental: arm) [default=auto]])],[req_asm=$withval], [req_asm=auto])

AC_ARG_WITH([ecmult-window], [AS_HELP_STRING([--with-ecmult-window=SIZE|auto],
[window size for ecmult precomputation for verification, specified as integer in range [2..24].]
[Larger values result in possibly better performance at the cost of an exponentially larger precomputed table.]
[The table will store 2^(SIZE-2) * 64 bytes of data but can be larger in memory due to platform-specific padding and alignment.]
[If the endomorphism optimization is enabled, two tables of this size are used instead of only one.]
["auto" is a reasonable setting for desktop machines (currently 15). [default=auto]]
)],
[req_ecmult_window=$withval], [req_ecmult_window=auto])

AC_CHECK_TYPES([__int128])

Expand Down Expand Up @@ -387,6 +396,28 @@ case $set_scalar in
;;
esac

#set ecmult window size
if test x"$req_ecmult_window" = x"auto"; then
set_ecmult_window=15
else
set_ecmult_window=$req_ecmult_window
fi

error_window_size=['window size for ecmult precomputation not an integer in range [2..24] or "auto"']
case $set_ecmult_window in
''|*[[!0-9]]*)
# no valid integer
AC_MSG_ERROR($error_window_size)
;;
*)
if test "$set_ecmult_window" -lt 2 -o "$set_ecmult_window" -gt 24 ; then
# not in range
AC_MSG_ERROR($error_window_size)
fi
AC_DEFINE_UNQUOTED(ECMULT_WINDOW_SIZE, $set_ecmult_window, [Set window size for ecmult precomputation])
;;
esac

if test x"$use_tests" = x"yes"; then
SECP_OPENSSL_CHECK
if test x"$has_openssl_ec" = x"yes"; then
Expand Down Expand Up @@ -516,6 +547,7 @@ echo " asm = $set_asm"
echo " bignum = $set_bignum"
echo " field = $set_field"
echo " scalar = $set_scalar"
echo " ecmult window size = $set_ecmult_window"
echo
echo " CC = $CC"
echo " CFLAGS = $CFLAGS"
Expand Down
1 change: 1 addition & 0 deletions src/basic-config.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@
#define USE_SCALAR_INV_BUILTIN 1
#define USE_FIELD_10X26 1
#define USE_SCALAR_8X32 1
#define ECMULT_WINDOW_SIZE 15

#endif /* USE_BASIC_CONFIG */

Expand Down
50 changes: 37 additions & 13 deletions src/ecmult_impl.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -30,16 +30,32 @@
# endif
#else
/* optimal for 128-bit and 256-bit exponents. */
#define WINDOW_A 5
/** larger numbers may result in slightly better performance, at the cost of
exponentially larger precomputed tables. */
#ifdef USE_ENDOMORPHISM
/** Two tables for window size 15: 1.375 MiB. */
#define WINDOW_G 15
#else
/** One table for window size 16: 1.375 MiB. */
#define WINDOW_G 16
# define WINDOW_A 5
/** Larger values for ECMULT_WINDOW_SIZE result in possibly better
* performance at the cost of an exponentially larger precomputed
* table. The exact table size is
* (1 << (WINDOW_G - 2)) * sizeof(secp256k1_ge_storage) bytes,
* where sizeof(secp256k1_ge_storage) is typically 64 bytes but can
* be larger due to platform-specific padding and alignment.
* If the endomorphism optimization is enabled (USE_ENDOMORMPHSIM)
* two tables of this size are used instead of only one.
*/
# define WINDOW_G ECMULT_WINDOW_SIZE
#endif

/* Noone will ever need more than a window size of 24. The code might
* be correct for larger values of ECMULT_WINDOW_SIZE but this is not
* not tested.
*
* The following limitations are known, and there are probably more:
* If WINDOW_G > 27 and size_t has 32 bits, then the code is incorrect
* because the size of the memory object that we allocate (in bytes)
* will not fit in a size_t.
* If WINDOW_G > 31 and int has 32 bits, then the code is incorrect
* because certain expressions will overflow.
*/
#if ECMULT_WINDOW_SIZE < 2 || ECMULT_WINDOW_SIZE > 24
# error Set ECMULT_WINDOW_SIZE to an integer in range [2..24].
#endif

#ifdef USE_ENDOMORPHISM
Expand Down Expand Up @@ -311,7 +327,12 @@ static void secp256k1_ecmult_context_build(secp256k1_ecmult_context *ctx, const
/* get the generator */
secp256k1_gej_set_ge(&gj, &secp256k1_ge_const_g);

ctx->pre_g = (secp256k1_ge_storage (*)[])checked_malloc(cb, sizeof((*ctx->pre_g)[0]) * ECMULT_TABLE_SIZE(WINDOW_G));
{
size_t size = sizeof((*ctx->pre_g)[0]) * ((size_t)ECMULT_TABLE_SIZE(WINDOW_G));
/* check for overflow */
VERIFY_CHECK(size / sizeof((*ctx->pre_g)[0]) == ((size_t)ECMULT_TABLE_SIZE(WINDOW_G)));
ctx->pre_g = (secp256k1_ge_storage (*)[])checked_malloc(cb, size);
}

/* precompute the tables with odd multiples */
secp256k1_ecmult_odd_multiples_table_storage_var(ECMULT_TABLE_SIZE(WINDOW_G), *ctx->pre_g, &gj);
Expand All @@ -321,7 +342,10 @@ static void secp256k1_ecmult_context_build(secp256k1_ecmult_context *ctx, const
secp256k1_gej g_128j;
int i;

ctx->pre_g_128 = (secp256k1_ge_storage (*)[])checked_malloc(cb, sizeof((*ctx->pre_g_128)[0]) * ECMULT_TABLE_SIZE(WINDOW_G));
size_t size = sizeof((*ctx->pre_g_128)[0]) * ((size_t) ECMULT_TABLE_SIZE(WINDOW_G));
/* check for overflow */
VERIFY_CHECK(size / sizeof((*ctx->pre_g_128)[0]) == ((size_t)ECMULT_TABLE_SIZE(WINDOW_G)));
ctx->pre_g_128 = (secp256k1_ge_storage (*)[])checked_malloc(cb, size);

/* calculate 2^128*generator */
g_128j = gj;
Expand All @@ -338,15 +362,15 @@ static void secp256k1_ecmult_context_clone(secp256k1_ecmult_context *dst,
if (src->pre_g == NULL) {
dst->pre_g = NULL;
} else {
size_t size = sizeof((*dst->pre_g)[0]) * ECMULT_TABLE_SIZE(WINDOW_G);
size_t size = sizeof((*dst->pre_g)[0]) * ((size_t)ECMULT_TABLE_SIZE(WINDOW_G));
dst->pre_g = (secp256k1_ge_storage (*)[])checked_malloc(cb, size);
memcpy(dst->pre_g, src->pre_g, size);
}
#ifdef USE_ENDOMORPHISM
if (src->pre_g_128 == NULL) {
dst->pre_g_128 = NULL;
} else {
size_t size = sizeof((*dst->pre_g_128)[0]) * ECMULT_TABLE_SIZE(WINDOW_G);
size_t size = sizeof((*dst->pre_g_128)[0]) * ((size_t)ECMULT_TABLE_SIZE(WINDOW_G));
dst->pre_g_128 = (secp256k1_ge_storage (*)[])checked_malloc(cb, size);
memcpy(dst->pre_g_128, src->pre_g_128, size);
}
Expand Down

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