diff --git a/.github/workflows/rust.yml b/.github/workflows/rust.yml
index 0f5e4c5..98ead0d 100644
--- a/.github/workflows/rust.yml
+++ b/.github/workflows/rust.yml
@@ -14,6 +14,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v4
+    - name: Setup toolchain
+      uses: dtolnay/rust-toolchain@master
+      with:
+        toolchain: nightly
+        components: rustfmt
     - name: Cache
       uses: actions/cache@v4.0.2
       with:
@@ -22,13 +27,7 @@ jobs:
           ~/.cargo/git
           ~/.rustup
           target
-        key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
-    - name: Setup toolchain
-      uses: actions-rs/toolchain@v1
-      with:
-        toolchain: nightly
-        override: true
-        components: rustfmt, clippy
+        key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}-${{steps.toolchain.outputs.name}}
     - name: Formatting
       run: cargo fmt --check
     - name: Build
diff --git a/Cargo.lock b/Cargo.lock
index f5894e7..99fab4a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -372,6 +372,7 @@ dependencies = [
 [[package]]
 name = "fftw"
 version = "0.8.0"
+source = "git+https://github.com/SallySoul/fftw3-rs.git?tag=fftw3-v0.8.1#ba98096fae4cc55e37f3deba19a5a696af551692"
 dependencies = [
  "bitflags 2.6.0",
  "fftw-sys",
@@ -385,6 +386,7 @@ dependencies = [
 [[package]]
 name = "fftw-src"
 version = "0.8.0"
+source = "git+https://github.com/SallySoul/fftw3-rs.git?tag=fftw3-v0.8.1#ba98096fae4cc55e37f3deba19a5a696af551692"
 dependencies = [
  "anyhow",
  "cc",
@@ -396,6 +398,7 @@ dependencies = [
 [[package]]
 name = "fftw-sys"
 version = "0.8.0"
+source = "git+https://github.com/SallySoul/fftw3-rs.git?tag=fftw3-v0.8.1#ba98096fae4cc55e37f3deba19a5a696af551692"
 dependencies = [
  "fftw-src",
  "libc",
diff --git a/Cargo.toml b/Cargo.toml
index b418bcc..b7b069e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,7 +5,7 @@ edition = "2021"
 
 [dependencies]
 colorous = "1.0.14"
-fftw = { path = "/Users/russell/projects/rust/fftw3-rs/fftw", features = ["system"] }
+fftw = { git = "https://github.com/SallySoul/fftw3-rs.git", tag = "fftw3-v0.8.1" }
 
 image = "0.25.2"
 num = "0.4.3"
diff --git a/examples/heat_2d_p_fft.rs b/examples/heat_2d_p_fft.rs
index af28d28..a3566d1 100644
--- a/examples/heat_2d_p_fft.rs
+++ b/examples/heat_2d_p_fft.rs
@@ -157,10 +157,6 @@ fn main() {
             fft_backwards_buffer[i] = fft_ic_output_buffer[i];
         }
 
-        for i in 0..width * height {
-            fft_ic_input_buffer[i] = 0.0;
-        }
-
         backward_plan
             .c2r(&mut fft_backwards_buffer, &mut fft_ic_input_buffer)
             .unwrap();
diff --git a/src/lib.rs b/src/lib.rs
index 01756ef..5d3da55 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,4 +5,5 @@ pub mod basic_domain;
 pub mod domain;
 pub mod linear_stencil;
 pub mod naive_solver;
+pub mod squaring;
 pub mod stencil;
diff --git a/src/squaring.rs b/src/squaring.rs
new file mode 100644
index 0000000..253737e
--- /dev/null
+++ b/src/squaring.rs
@@ -0,0 +1,55 @@
+pub fn log2ceil(i: usize) -> usize {
+    (usize::BITS - i.leading_zeros()) as usize
+}
+
+pub fn repeated_square(exp0: usize, i: usize) -> usize {
+    let mut exp = exp0;
+    let mut squares = i;
+    let mut result = 1;
+    let n = log2ceil(exp0);
+    println!(
+        "repeated, n: {}, exp: {}, result: {}, squares: {}",
+        n, exp, result, squares
+    );
+    for _ in 0..n {
+        if exp % 2 == 1 {
+            result *= squares;
+            exp -= 1;
+            println!(
+                "  - odd exp, result: {}, squares: {}, exp: {}",
+                result, squares, exp
+            );
+        }
+        exp /= 2;
+        squares *= squares;
+        println!(" * exp: {}, result: {}, squares: {}", exp, result, squares);
+    }
+
+    result
+}
+
+#[cfg(test)]
+mod unit_tests {
+    use super::*;
+
+    #[test]
+    fn log2ceil_test() {
+        assert_eq!(log2ceil(1), 1);
+        assert_eq!(log2ceil(2), 2);
+        assert_eq!(log2ceil(3), 2);
+        assert_eq!(log2ceil(4), 3);
+        assert_eq!(log2ceil(5), 3);
+        assert_eq!(log2ceil(6), 3);
+        assert_eq!(log2ceil(7), 3);
+        assert_eq!(log2ceil(8), 4);
+    }
+
+    #[test]
+    fn repeated_square_test() {
+        assert_eq!(repeated_square(2, 2), 4);
+        assert_eq!(repeated_square(3, 2), 8);
+        assert_eq!(repeated_square(4, 2), 16);
+        assert_eq!(repeated_square(5, 2), 32);
+        assert_eq!(repeated_square(9, 3), 19683);
+    }
+}