Adding U to the magic constants ensures that we are not mixing unsigned and signed value during multiplication, and ensures that the multiplication will not be subject to integer promotion.
The (uint32_t)/(uint64_t) casts ensure the values are properly truncated no matter the size of an int.
Prior to this commit, if secp256k1_ctz32_var_debruijn were some how managed to be built on a platform with 64-bit ints, (though this function is specifically only intended to be used on 32-bit platforms) it would perform an out-of-bounds array access.
ce60785b2654e60b43577dd75996b7020afbfec8 Introduce SECP256K1_B macro for curve b coefficient (Pieter Wuille)
4934aa79958b506a6e9cfcfe30a8f685db3f5f5f Switch to exhaustive groups with small B coefficient (Pieter Wuille)
Pull request description:
This has the advantage that in the future, multiplication with B can be done using `secp256k1_fe_mul_int` rather than the slower `secp256k1_fe_mul`.
ACKs for top commit:
real-or-random:
ACK ce60785b2654e60b43577dd75996b7020afbfec8 also ran the exhaustive tests with the group of size 7
apoelstra:
ACK ce60785b2654e60b43577dd75996b7020afbfec8
Tree-SHA512: 006041189d18319ddb9c0ed54e479f393b83ab2a368d198bd24860d1d2574c0c1a311aea24fbef2e74bb7859a687dfc803b9e963e6dc5c61cb707e20f52b5a70
d21647520532957a78027be1ab606b814a2ec720 test secp256k1_i128_to_i64 (Russell O'Connor)
4bc429019dc4bff6af0f9824ad6ab6745f09f8ba Add a secp256k1_i128_to_u64 function. (Russell O'Connor)
Pull request description:
I wanted to experiment with what would be required to split up `secp256k1_i128_to_i64` between those cases when a signed 64 bit value is being demoted, versus an unsigned 64 bit value is being extracted from the lower bits, and this is the result.
I'm not sure this is a useful PR, so feel free to close it. However, since it is already written, I figured it is worth at least discussing.
ACKs for top commit:
sipa:
utACK d21647520532957a78027be1ab606b814a2ec720
real-or-random:
ACK d21647520532957a78027be1ab606b814a2ec720
Tree-SHA512: 41dbb1d33b3078bee8e71a838cfad6f1859c0bba602ae061259add8e9e8ea5aa482daa41de79dbd7433ddbef4a0bc52757f3c45d63acc9c0eb05aa3ca891b922
This change eases the use of alternate build systems by moving
the variables in `src/libsecp256k1-config.h` to compiler macros
for each invocation, preventing duplication of these variables
for each build system.
Co-authored-by: Ali Sherief <ali@notatether.com>
a340d9500a9c45e5c261174f48b3eb18b3b3647d ci: add int128_struct tests (Jonas Nick)
dceaa1f57963d1a88b24974eab4b49baac6d04cd int128: Tidy #includes of int128.h and int128_impl.h (Tim Ruffing)
2914bccbc0913806ee64425a27d38cdc27b288e8 Simulated int128 type. (Russell O'Connor)
Pull request description:
Abstracts the int128 type and provides an native version, if available, or a implements it using a pair of int64_t's.
This is activated by setting the configuration flag `--with-test-override-wide-multiply=int128_struct`.
The primary purpose of this PR is to take advantage of MSVC's [umulh](https://docs.microsoft.com/en-us/cpp/intrinsics/umulh?view=msvc-170) intrinsic that we can use to simulate an int128 type which MSVC does not have (AFAIU). This PR lays out the groundwork for this level of MSVC support, but doesn't include the configuration logic to enable it yet.
For completeness, and implementation of `umulh` and `mulh` are also provided for compilers that support neither the intrinsic nor the int128 type (such as CompCert?). This also opens up the possibility of removing the 32-bit field and scalar implementations should that ever be desired.
ACKs for top commit:
sipa:
ACK a340d9500a9c45e5c261174f48b3eb18b3b3647d
jonasnick:
ACK a340d9500a9c45e5c261174f48b3eb18b3b3647d
Tree-SHA512: b4f2853fa3ab60ce9d77b4eaee1fd20c4b612850e19fcb3179d7e36986f420c6c4589ff72f0cf844f989584ace49a1cd23cca3f4e405dabefc8da647a0df679d
After this commit, int128.h and int128_impl.h are included as follows:
- .c files which use int128 include int128_impl.h (after util.h)
- .h files which use int128 include int128.h (after util.h)
This list is exhaustive. util.h needs to included first because it sets
up necessary #defines.
