From 62b9f06104889fd99e889908a813ac7210e0bf12 Mon Sep 17 00:00:00 2001
From: "Wladimir J. van der Laan" <laanwj@gmail.com>
Date: Wed, 7 Aug 2019 18:00:35 +0000
Subject: [PATCH] build.rs: Add feature 'lowmemory' to reduce memory usage

Currently, this only set `ECMULT_WINDOW_SIZE` to 4 instead of 15.

Fixes #139.

fixup
---
 .travis.yml  | 1 +
 CHANGELOG.md | 7 +++++++
 Cargo.toml   | 1 +
 build.rs     | 8 ++++++--
 4 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/.travis.yml b/.travis.yml
index 5554a38..084a2ac 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -30,6 +30,7 @@ script:
   - cargo build --verbose --no-default-features --features="rand"
   - cargo build --verbose --no-default-features --features="rand serde recovery endomorphism"
   - cargo build --verbose --no-default-features --features="fuzztarget recovery"
+  - cargo build --verbose --no-default-features --features="lowmemory"
   - cargo build --verbose
   - cargo test --verbose
   - cargo build --release
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 93f41d2..8f913bf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,10 @@
+# 0.15.1 - ????-??-??
+
+- Add feature `lowmemory` that reduces the EC mult window size to require
+  significantly less memory for the validation context (~340B instead of
+  ~520kB), at the cost of slower validation. It does not affect signing, nor
+  the size of the signing context.
+
 # 0.15.0 - 2019-07-25
 
 * Implement hex human-readable serde for PublicKey
diff --git a/Cargo.toml b/Cargo.toml
index e0090ca..4ee277b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -32,6 +32,7 @@ fuzztarget = []
 std = ["rand/std"]
 recovery = []
 endomorphism = []
+lowmemory = []
 
 [dev-dependencies]
 rand = "0.6"
diff --git a/build.rs b/build.rs
index 86d8125..3e11c59 100644
--- a/build.rs
+++ b/build.rs
@@ -53,9 +53,13 @@ fn main() {
                .define("USE_FIELD_INV_BUILTIN", Some("1"))
                .define("USE_SCALAR_INV_BUILTIN", Some("1"))
                .define("ENABLE_MODULE_ECDH", Some("1"))
-               .define("USE_EXTERNAL_DEFAULT_CALLBACKS", Some("1"))
-               .define("ECMULT_WINDOW_SIZE", Some("15")); // This is the default in the configure file (`auto`)
+               .define("USE_EXTERNAL_DEFAULT_CALLBACKS", Some("1"));
 
+    if cfg!(feature = "lowmemory") {
+        base_config.define("ECMULT_WINDOW_SIZE", Some("4")); // A low-enough value to consume neglible memory
+    } else {
+        base_config.define("ECMULT_WINDOW_SIZE", Some("15")); // This is the default in the configure file (`auto`)
+    }
     #[cfg(feature = "endomorphism")]
     base_config.define("USE_ENDOMORPHISM", Some("1"));
     #[cfg(feature = "recovery")]