From 5a27abab52500f23431b71d9592631b39a4bc84b Mon Sep 17 00:00:00 2001
From: Andrew Poelstra <apoelstra@wpsoftware.net>
Date: Mon, 30 Jul 2018 03:11:43 +0000
Subject: [PATCH 1/2] switch to 64-bit compilation; add flag for 32-bit

---
 CHANGELOG.md             |  1 +
 build.rs                 | 26 ++++++++++++++++++++++----
 depend/check_uint128_t.c | 16 ++++++++++++++++
 3 files changed, 39 insertions(+), 4 deletions(-)
 create mode 100644 depend/check_uint128_t.c

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e027ac5..bbc9a18 100644
--- a/CHANGELOG.md
+++ b/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
 
diff --git a/build.rs b/build.rs
index 29aac07..f257106 100644
--- a/build.rs
+++ b/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")
diff --git a/depend/check_uint128_t.c b/depend/check_uint128_t.c
new file mode 100644
index 0000000..4d90955
--- /dev/null
+++ b/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;
+}
+

From 5cd45333754bd57d90543dcb1ab25232c6f40381 Mon Sep 17 00:00:00 2001
From: Andrew Poelstra <apoelstra@wpsoftware.net>
Date: Tue, 21 Aug 2018 18:41:42 +0000
Subject: [PATCH 2/2] add warning if uint128_t detection fails

---
 build.rs | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/build.rs b/build.rs
index f257106..8175c82 100644
--- a/build.rs
+++ b/build.rs
@@ -23,14 +23,23 @@
 
 extern crate cc;
 
+use std::io::{self, Write};
+
 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()
+        let check = cc::Build::new().file("depend/check_uint128_t.c")
+                                    .cargo_metadata(false)
+                                    .try_compile("check_uint128_t")
+                                    .is_ok();
+        if !check {
+            writeln!(
+                &mut io::stderr(),
+                "Warning: Compiling in 32-bit mode on a 64-bit architecture due to lack of uint128_t support."
+            ).expect("print to stderr")
+        }
+        check
     };
     #[cfg(not(target_pointer_width = "64"))]
     let use_64bit_compilation = false;