Replace gmpxx usage with gmp

The packaging isn't looking for gmpxx, and so fails when gmp is
installed but gmpxx isn't.  Rather than add a dependency on both gmpxx
and gmp, this just replaces the small amount of gmpxx usage with gmp and
drops the gmpxx linking.

Also fixes cmake target names to be less error prone (using gmp::gmp
rather than bare gmp or gmpxx ensures cmake sees a missing target rather
than it failing later at build time), and to not do anything if a
gmp::gmp target is already available (e.g. from a parent project).

CMakeLists.txt

@@ -106,8 +106,7 @@ target_link_libraries(
   PRIVATE
     cpr::cpr
     oxen::logging
-    gmp
-    gmpxx
+    gmp::gmp
 )
 if(${PROJECT_NAME}_ENABLE_SIGNER)
     target_link_libraries(${PROJECT_NAME} PUBLIC secp256k1)

external/CMakeLists.txt

@@ -62,7 +62,8 @@ endif()
 # GMP
 #
 
-pkg_check_modules(GMP gmp IMPORTED_TARGET REQUIRED)
-add_library(gmp INTERFACE)
-target_link_libraries(gmp INTERFACE PkgConfig::GMP)
-message(STATUS "Found gmp ${GMP_VERSION}")
+if(NOT TARGET gmp::gmp)
+    pkg_check_modules(GMP gmp IMPORTED_TARGET REQUIRED GLOBAL)
+    add_library(gmp::gmp ALIAS PkgConfig::GMP)
+    message(STATUS "Found gmp ${GMP_VERSION}")
+endif()

src/provider.cpp

@@ -15,7 +15,7 @@
 #include "ethyl/provider.hpp"
 #include "ethyl/utils.hpp"
 
-#include <gmpxx.h>
+#include <gmp.h>
 
 namespace
 {
@@ -704,22 +704,23 @@ void Provider::getBalanceAsync(std::string_view address, optional_callback<std::
             return;
         }
 
-        try
-        {
-            std::string balanceHex = r->get<std::string>();
+        std::string balanceHex = r->get<std::string>();
 
-            // Convert balance from hex to GMP multi-precision integer
-            mpz_class balance;
-            balance.set_str(balanceHex, 0); // 0 as base to automatically pick up hex from the prepended 0x of our balanceHex string
+        // Convert balance from hex to GMP multi-precision integer
 
-            user_cb(balance.get_str());
-            return;
-        }
-        catch (const std::exception& e)
-        {
-            log::warning(logcat, "eth_getBalance response, failed to parse bigint: {}", r->get<std::string>());
-            user_cb(std::nullopt);
+        std::optional<std::string> bal10;
+        mpz_t balance;
+        // 0 as base to automatically pick up hex from the prepended 0x of our balanceHex string
+        if (int rc = mpz_init_set_str(balance, balanceHex.c_str(), 0); rc == 0) {
+            bal10.emplace();
+            bal10->resize(mpz_sizeinbase(balance, 10) + 1);
+            mpz_get_str(bal10->data(), 10, balance);
+            bal10->resize(std::strlen(bal10->c_str()));
+        } else {
+            log::warning(logcat, "eth_getBalance response, failed to parse bigint: {}", balanceHex);
         }
+        mpz_clear(balance);
+        user_cb(std::move(bal10));
     };
     makeJsonRpcRequest("eth_getBalance", params, std::move(cb));
 }