switch to 64-bit compilation; add flag for 32-bit

CHANGELOG.md

@@ -3,6 +3,7 @@
 
 * Update `rand` to 0.4 and `gcc` 0.3 to `cc` 1.0. (`rand` 0.5 exists but has a lot of breaking changes and no longer compiles with 1.14.0.)
 * Remove `PublicKey::combine` from API since it cannot be used with anything else in the API
+* Detect whether 64-bit compilation is possible, and do it if we can (big performance improvement)
 
 # 0.10.0 - 2018-07-25
 

build.rs

@@ -24,6 +24,19 @@
 extern crate cc;
 
 fn main() {
+    // Check whether we can use 64-bit compilation
+    #[cfg(target_pointer_width = "64")]
+    let use_64bit_compilation = {
+        cc::Build::new().file("depend/check_uint128_t.c")
+                        .cargo_metadata(false)
+                        .try_compile("check_uint128_t")
+                        .is_ok()
+    };
+    #[cfg(not(target_pointer_width = "64"))]
+    let use_64bit_compilation = false;
+
+
+    // Actual build
     let mut base_config = cc::Build::new();
     base_config.include("depend/secp256k1/")
                .include("depend/secp256k1/include")
@@ -35,14 +48,19 @@ fn main() {
                .define("USE_NUM_NONE", Some("1"))
                .define("USE_FIELD_INV_BUILTIN", Some("1"))
                .define("USE_SCALAR_INV_BUILTIN", Some("1"))
-               // TODO these should use 64-bit variants on 64-bit systems
-               .define("USE_FIELD_10X26", Some("1"))
-               .define("USE_SCALAR_8X32", Some("1"))
                .define("USE_ENDOMORPHISM", Some("1"))
-               // These all are OK.
                .define("ENABLE_MODULE_ECDH", Some("1"))
                .define("ENABLE_MODULE_RECOVERY", Some("1"));
 
+    if use_64bit_compilation {
+        base_config.define("USE_FIELD_5X52", Some("1"))
+                   .define("USE_SCALAR_4X64", Some("1"))
+                   .define("HAVE___INT128", Some("1"));
+    } else {
+        base_config.define("USE_FIELD_10X26", Some("1"))
+                   .define("USE_SCALAR_8X32", Some("1"));
+    }
+
     // secp256k1
     base_config.file("depend/secp256k1/contrib/lax_der_parsing.c")
                .file("depend/secp256k1/src/secp256k1.c")

depend/check_uint128_t.c

@@ -0,0 +1,16 @@
+
+#include <stdint.h>
+
+int main(void) {
+    __uint128_t var_128;
+    uint64_t var_64;
+
+    /* Try to shut up "unused variable" warnings */
+    var_64 = 100;
+    var_128 = 100;
+    if (var_64 == var_128) {
+        var_64 = 20;
+    }
+    return 0;
+}
+