precompiles: Implement expmod with GMP

Author: chfast

cmake/FindGMP.cmake

@@ -0,0 +1,25 @@
+# evmone: Fast Ethereum Virtual Machine implementation
+# Copyright 2025 The evmone Authors.
+# SPDX-License-Identifier: Apache-2.0
+
+# Finds the GMP or MPIR library and its include directories.
+
+find_library(GMP_LIBRARY NAMES gmp mpir DOC "GMP/MPIR library")
+find_path(GMP_INCLUDE_DIR NAMES gmp.h DOC "GMP header")
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(
+    GMP
+    REQUIRED_VARS GMP_LIBRARY GMP_INCLUDE_DIR
+)
+
+if(GMP_FOUND)
+    if(NOT TARGET GMP::gmp)
+        add_library(GMP::gmp UNKNOWN IMPORTED)
+        set_target_properties(GMP::gmp PROPERTIES
+            IMPORTED_LOCATION ${GMP_LIBRARY}
+            IMPORTED_LINK_INTERFACE_LANGUAGES C
+            INTERFACE_INCLUDE_DIRECTORIES ${GMP_INCLUDE_DIR}
+        )
+    endif()
+endif()

test/state/CMakeLists.txt

@@ -72,3 +72,16 @@ if(EVMONE_PRECOMPILES_SILKPRE)
         precompiles_silkpre.cpp
     )
 endif()
+
+# This is done after Silkpre because it also tries to find GMP.
+option(EVMONE_PRECOMPILES_GMP "Enable precompiles implementations via the GMP/MPIR library" ON)
+if(EVMONE_PRECOMPILES_GMP)
+    find_package(GMP REQUIRED)
+    target_link_libraries(evmone-state PRIVATE GMP::gmp)
+    target_compile_definitions(evmone-state PRIVATE EVMONE_PRECOMPILES_GMP=1)
+    target_sources(
+        evmone-state PRIVATE
+        precompiles_gmp.hpp
+        precompiles_gmp.cpp
+    )
+endif()

test/state/precompiles.cpp

@@ -19,8 +19,8 @@
 #include <limits>
 #include <span>
 
-#ifdef EVMONE_PRECOMPILES_SILKPRE
-#include "precompiles_silkpre.hpp"
+#ifdef EVMONE_PRECOMPILES_GMP
+#include "precompiles_gmp.hpp"
 #endif
 
 namespace evmone::state
@@ -363,16 +363,12 @@ ExecutionResult expmod_execute(
     const auto exp = payload.substr(base_len, exp_len);
     const auto mod = mod_requires_padding ? bytes_view{output, mod_len} : mod_explicit;
 
-#ifdef EVMONE_PRECOMPILES_SILKPRE
-    (void)base;
-    (void)exp;
-    (void)mod;
-    // For Silkpre use the raw input for compatibility.
-    return silkpre_expmod_execute(input, input_size, output, output_size);
+#ifdef EVMONE_PRECOMPILES_GMP
+    expmod_gmp(base, exp, mod, output);
 #else
     expmod_stub(base, exp, mod, output);
-    return {EVMC_SUCCESS, mod.size()};
 #endif
+    return {EVMC_SUCCESS, mod.size()};
 }
 
 ExecutionResult ecadd_execute(const uint8_t* input, size_t input_size, uint8_t* output,

test/state/precompiles_gmp.cpp

@@ -0,0 +1,30 @@
+// evmone: Fast Ethereum Virtual Machine implementation
+// Copyright 2025 The evmone Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+#include "precompiles_gmp.hpp"
+#include <gmp.h>
+#include <cassert>
+
+namespace evmone::state
+{
+void expmod_gmp(bytes_view base, bytes_view exp, bytes_view mod, uint8_t* output) noexcept
+{
+    mpz_t b, e, m, r;  // NOLINT(*-isolate-declaration)
+    mpz_inits(b, e, m, r, nullptr);
+    mpz_import(b, base.size(), 1, 1, 0, 0, base.data());
+    mpz_import(e, exp.size(), 1, 1, 0, 0, exp.data());
+    mpz_import(m, mod.size(), 1, 1, 0, 0, mod.data());
+    assert(mpz_sgn(m) != 0);
+
+    mpz_powm(r, b, e, m);
+
+    size_t export_size = 0;
+    mpz_export(output, &export_size, 1, 1, 0, 0, r);
+    assert(export_size <= mod.size());
+    mpz_clears(b, e, m, r, nullptr);
+
+    std::copy_backward(output, output + export_size, output + mod.size());
+    std::fill_n(output, mod.size() - export_size, 0);
+}
+}  // namespace evmone::state

test/state/precompiles_gmp.hpp

@@ -0,0 +1,14 @@
+// evmone: Fast Ethereum Virtual Machine implementation
+// Copyright 2025 The evmone Authors.
+// SPDX-License-Identifier: Apache-2.0
+#pragma once
+
+#include <evmc/evmc.hpp>
+
+namespace evmone::state
+{
+using evmc::bytes_view;
+
+/// Executes the expmod precompile using the GMP library.
+void expmod_gmp(bytes_view base, bytes_view exp, bytes_view mod, uint8_t* output) noexcept;
+}  // namespace evmone::state