ferrotorch-cubecl 0.4.0

//! Portable GPU operations that dispatch through a real CubeCL
//! [`ComputeClient`] and run `#[cube]` kernels on the selected backend.
//!
//! Each function takes a [`CubeRuntime`] (which owns the client) and a pair
//! of `f32` tensors, uploads the inputs to device memory, launches the
//! kernel, and reads the result back into a new CPU-resident tensor. This
//! mirrors what `ferrotorch-gpu` does for eager execution and lets us share
//! the same API across CUDA, ROCm, and WGPU.
//!
//! Only `f32` is supported today — CubeCL's `Float` trait requires
//! `CubeElement`, which `f32` implements on every backend. Adding `f16` /
//! `bf16` is a drop-in extension once the CubeCL support matures.

use ferrotorch_core::{FerrotorchError, FerrotorchResult, Tensor};

use crate::runtime::CubeRuntime;

// When a backend feature is enabled we pull in the kernels, the
// dispatcher macros, and the client enum. Without a feature we leave the
// module empty and every public op returns `DeviceUnavailable`. That matches
// the contract of `CubeRuntime::new`, which itself errors out in no-backend
// builds.
#[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
use ferrotorch_core::from_vec;

#[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
use crate::kernels;
#[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
use crate::runtime::CubeClient;

// ---------------------------------------------------------------------------
// Shape helpers (always available so error paths can use them)
// ---------------------------------------------------------------------------

fn check_same_shape(a: &Tensor<f32>, b: &Tensor<f32>) -> FerrotorchResult<()> {
    if a.shape() != b.shape() {
        return Err(FerrotorchError::ShapeMismatch {
            message: format!(
                "cubecl elementwise: lhs {:?} vs rhs {:?}",
                a.shape(),
                b.shape()
            ),
        });
    }
    Ok(())
}

#[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
fn contiguous_data(t: &Tensor<f32>) -> FerrotorchResult<Vec<f32>> {
    // `data()` only works on contiguous tensors; fall back to `data_vec()`
    // otherwise.
    match t.data() {
        Ok(slice) => Ok(slice.to_vec()),
        Err(_) => t.data_vec(),
    }
}

// ---------------------------------------------------------------------------
// Dispatcher macros — one per op signature, only defined when a backend is
// present so they can expand without unreachable arms.
// ---------------------------------------------------------------------------

#[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
macro_rules! dispatch_binary {
    ($rt:expr, $launcher:path, $a:expr, $b:expr) => {{
        match $rt.client() {
            #[cfg(feature = "wgpu")]
            CubeClient::Wgpu(c) => $launcher(c, $a, $b),
            #[cfg(feature = "cuda")]
            CubeClient::Cuda(c) => $launcher(c, $a, $b),
            #[cfg(feature = "rocm")]
            CubeClient::Rocm(c) => $launcher(c, $a, $b),
        }
    }};
}

#[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
macro_rules! dispatch_unary {
    ($rt:expr, $launcher:path, $x:expr) => {{
        match $rt.client() {
            #[cfg(feature = "wgpu")]
            CubeClient::Wgpu(c) => $launcher(c, $x),
            #[cfg(feature = "cuda")]
            CubeClient::Cuda(c) => $launcher(c, $x),
            #[cfg(feature = "rocm")]
            CubeClient::Rocm(c) => $launcher(c, $x),
        }
    }};
}

#[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
macro_rules! dispatch_matmul {
    ($rt:expr, $a:expr, $b:expr, $m:expr, $k:expr, $n:expr) => {{
        match $rt.client() {
            #[cfg(feature = "wgpu")]
            CubeClient::Wgpu(c) => kernels::run_matmul(c, $a, $b, $m, $k, $n),
            #[cfg(feature = "cuda")]
            CubeClient::Cuda(c) => kernels::run_matmul(c, $a, $b, $m, $k, $n),
            #[cfg(feature = "rocm")]
            CubeClient::Rocm(c) => kernels::run_matmul(c, $a, $b, $m, $k, $n),
        }
    }};
}

// ---------------------------------------------------------------------------
// Public ops — one implementation per backend-enabled build, one no-op
// error stub for the no-backend build.
// ---------------------------------------------------------------------------

/// Elementwise `a + b` on the GPU.
#[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
pub fn portable_add(
    a: &Tensor<f32>,
    b: &Tensor<f32>,
    rt: &CubeRuntime,
) -> FerrotorchResult<Tensor<f32>> {
    check_same_shape(a, b)?;
    let a_data = contiguous_data(a)?;
    let b_data = contiguous_data(b)?;
    let out = dispatch_binary!(rt, kernels::run_add, &a_data, &b_data);
    from_vec(out, a.shape())
}

#[cfg(not(any(feature = "wgpu", feature = "cuda", feature = "rocm")))]
pub fn portable_add(
    a: &Tensor<f32>,
    b: &Tensor<f32>,
    _rt: &CubeRuntime,
) -> FerrotorchResult<Tensor<f32>> {
    check_same_shape(a, b)?;
    Err(FerrotorchError::DeviceUnavailable)
}

/// Elementwise `a - b` on the GPU.
#[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
pub fn portable_sub(
    a: &Tensor<f32>,
    b: &Tensor<f32>,
    rt: &CubeRuntime,
) -> FerrotorchResult<Tensor<f32>> {
    check_same_shape(a, b)?;
    let a_data = contiguous_data(a)?;
    let b_data = contiguous_data(b)?;
    let out = dispatch_binary!(rt, kernels::run_sub, &a_data, &b_data);
    from_vec(out, a.shape())
}

#[cfg(not(any(feature = "wgpu", feature = "cuda", feature = "rocm")))]
pub fn portable_sub(
    a: &Tensor<f32>,
    b: &Tensor<f32>,
    _rt: &CubeRuntime,
) -> FerrotorchResult<Tensor<f32>> {
    check_same_shape(a, b)?;
    Err(FerrotorchError::DeviceUnavailable)
}

/// Elementwise `a * b` on the GPU.
#[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
pub fn portable_mul(
    a: &Tensor<f32>,
    b: &Tensor<f32>,
    rt: &CubeRuntime,
) -> FerrotorchResult<Tensor<f32>> {
    check_same_shape(a, b)?;
    let a_data = contiguous_data(a)?;
    let b_data = contiguous_data(b)?;
    let out = dispatch_binary!(rt, kernels::run_mul, &a_data, &b_data);
    from_vec(out, a.shape())
}

#[cfg(not(any(feature = "wgpu", feature = "cuda", feature = "rocm")))]
pub fn portable_mul(
    a: &Tensor<f32>,
    b: &Tensor<f32>,
    _rt: &CubeRuntime,
) -> FerrotorchResult<Tensor<f32>> {
    check_same_shape(a, b)?;
    Err(FerrotorchError::DeviceUnavailable)
}

/// Elementwise `relu(x)` on the GPU.
#[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
pub fn portable_relu(x: &Tensor<f32>, rt: &CubeRuntime) -> FerrotorchResult<Tensor<f32>> {
    let x_data = contiguous_data(x)?;
    let out = dispatch_unary!(rt, kernels::run_relu, &x_data);
    from_vec(out, x.shape())
}

#[cfg(not(any(feature = "wgpu", feature = "cuda", feature = "rocm")))]
pub fn portable_relu(_x: &Tensor<f32>, _rt: &CubeRuntime) -> FerrotorchResult<Tensor<f32>> {
    Err(FerrotorchError::DeviceUnavailable)
}

/// 2-D matrix multiplication on the GPU.
///
/// `a` must have shape `[M, K]` and `b` must have shape `[K, N]`. The
/// result has shape `[M, N]`.
#[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
pub fn portable_matmul(
    a: &Tensor<f32>,
    b: &Tensor<f32>,
    rt: &CubeRuntime,
) -> FerrotorchResult<Tensor<f32>> {
    let (m, k, n) = check_matmul_shapes(a, b)?;
    let a_data = contiguous_data(a)?;
    let b_data = contiguous_data(b)?;
    let out = dispatch_matmul!(rt, &a_data, &b_data, m, k, n);
    from_vec(out, &[m, n])
}

#[cfg(not(any(feature = "wgpu", feature = "cuda", feature = "rocm")))]
pub fn portable_matmul(
    a: &Tensor<f32>,
    b: &Tensor<f32>,
    _rt: &CubeRuntime,
) -> FerrotorchResult<Tensor<f32>> {
    check_matmul_shapes(a, b)?;
    Err(FerrotorchError::DeviceUnavailable)
}

fn check_matmul_shapes(
    a: &Tensor<f32>,
    b: &Tensor<f32>,
) -> FerrotorchResult<(usize, usize, usize)> {
    let a_shape = a.shape();
    let b_shape = b.shape();
    if a_shape.len() != 2 || b_shape.len() != 2 {
        return Err(FerrotorchError::ShapeMismatch {
            message: format!(
                "cubecl matmul requires 2-D tensors, got lhs {:?} rhs {:?}",
                a_shape, b_shape
            ),
        });
    }
    if a_shape[1] != b_shape[0] {
        return Err(FerrotorchError::ShapeMismatch {
            message: format!(
                "cubecl matmul inner dims mismatch: lhs {:?} vs rhs {:?}",
                a_shape, b_shape
            ),
        });
    }
    Ok((a_shape[0], a_shape[1], b_shape[1]))
}

// ---------------------------------------------------------------------------
// Additional elementwise ops — macro-generated for brevity
// ---------------------------------------------------------------------------

macro_rules! define_portable_unary {
    ($name:ident, $runner:ident) => {
        #[doc = concat!("Elementwise `", stringify!($name), "(x)` on the GPU.")]
        #[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
        pub fn $name(x: &Tensor<f32>, rt: &CubeRuntime) -> FerrotorchResult<Tensor<f32>> {
            let x_data = contiguous_data(x)?;
            let out = dispatch_unary!(rt, kernels::$runner, &x_data);
            from_vec(out, x.shape())
        }

        #[cfg(not(any(feature = "wgpu", feature = "cuda", feature = "rocm")))]
        pub fn $name(_x: &Tensor<f32>, _rt: &CubeRuntime) -> FerrotorchResult<Tensor<f32>> {
            Err(FerrotorchError::DeviceUnavailable)
        }
    };
}

macro_rules! define_portable_binary {
    ($name:ident, $runner:ident) => {
        #[doc = concat!("Elementwise `a ", stringify!($name), " b` on the GPU.")]
        #[cfg(any(feature = "wgpu", feature = "cuda", feature = "rocm"))]
        pub fn $name(
            a: &Tensor<f32>,
            b: &Tensor<f32>,
            rt: &CubeRuntime,
        ) -> FerrotorchResult<Tensor<f32>> {
            check_same_shape(a, b)?;
            let a_data = contiguous_data(a)?;
            let b_data = contiguous_data(b)?;
            let out = dispatch_binary!(rt, kernels::$runner, &a_data, &b_data);
            from_vec(out, a.shape())
        }

        #[cfg(not(any(feature = "wgpu", feature = "cuda", feature = "rocm")))]
        pub fn $name(
            a: &Tensor<f32>,
            b: &Tensor<f32>,
            _rt: &CubeRuntime,
        ) -> FerrotorchResult<Tensor<f32>> {
            check_same_shape(a, b)?;
            Err(FerrotorchError::DeviceUnavailable)
        }
    };
}

define_portable_binary!(portable_div, run_div);

define_portable_unary!(portable_neg, run_neg);
define_portable_unary!(portable_abs, run_abs);
define_portable_unary!(portable_exp, run_exp);
define_portable_unary!(portable_ln, run_ln);
define_portable_unary!(portable_sqrt, run_sqrt);
define_portable_unary!(portable_sin, run_sin);
define_portable_unary!(portable_cos, run_cos);
define_portable_unary!(portable_tanh, run_tanh);
define_portable_unary!(portable_sigmoid, run_sigmoid);

// ---------------------------------------------------------------------------
// Tests — only meaningful with a real backend feature
// ---------------------------------------------------------------------------

#[cfg(all(test, feature = "wgpu"))]
mod tests {
    use super::*;
    use crate::runtime::CubeDevice;

    fn runtime() -> CubeRuntime {
        CubeRuntime::new(CubeDevice::Wgpu(0)).expect("wgpu runtime init")
    }

    #[test]
    fn portable_add_runs_on_gpu() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[1.0_f32, 2.0, 3.0, 4.0]).unwrap();
        let b = ferrotorch_core::tensor(&[10.0_f32, 20.0, 30.0, 40.0]).unwrap();
        let c = portable_add(&a, &b, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        assert_eq!(data, &[11.0, 22.0, 33.0, 44.0]);
    }

    #[test]
    fn portable_sub_runs_on_gpu() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[10.0_f32, 20.0, 30.0]).unwrap();
        let b = ferrotorch_core::tensor(&[1.0_f32, 2.0, 3.0]).unwrap();
        let c = portable_sub(&a, &b, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        assert_eq!(data, &[9.0, 18.0, 27.0]);
    }

    #[test]
    fn portable_mul_runs_on_gpu() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[2.0_f32, 3.0, 4.0]).unwrap();
        let b = ferrotorch_core::tensor(&[10.0_f32, 10.0, 10.0]).unwrap();
        let c = portable_mul(&a, &b, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        assert_eq!(data, &[20.0, 30.0, 40.0]);
    }

    #[test]
    fn portable_relu_runs_on_gpu() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[-3.0_f32, -1.0, 0.0, 1.0, 3.0]).unwrap();
        let c = portable_relu(&a, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        assert_eq!(data, &[0.0, 0.0, 0.0, 1.0, 3.0]);
    }

    #[test]
    fn portable_matmul_runs_on_gpu() {
        let rt = runtime();
        // A = [[1, 2, 3], [4, 5, 6]]  (2x3)
        // B = [[7, 8], [9, 10], [11, 12]]  (3x2)
        // C = [[58, 64], [139, 154]]  (2x2)
        let a = ferrotorch_core::from_vec(vec![1.0_f32, 2.0, 3.0, 4.0, 5.0, 6.0], &[2, 3]).unwrap();
        let b =
            ferrotorch_core::from_vec(vec![7.0_f32, 8.0, 9.0, 10.0, 11.0, 12.0], &[3, 2]).unwrap();
        let c = portable_matmul(&a, &b, &rt).unwrap();
        assert_eq!(c.shape(), &[2, 2]);
        let data: &[f32] = c.data().unwrap();
        assert!((data[0] - 58.0).abs() < 1e-4);
        assert!((data[1] - 64.0).abs() < 1e-4);
        assert!((data[2] - 139.0).abs() < 1e-4);
        assert!((data[3] - 154.0).abs() < 1e-4);
    }

    #[test]
    fn portable_matmul_rejects_rank_mismatch() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[1.0_f32, 2.0, 3.0]).unwrap();
        let b = ferrotorch_core::from_vec(vec![1.0_f32, 2.0, 3.0], &[3, 1]).unwrap();
        let err = portable_matmul(&a, &b, &rt).unwrap_err();
        assert!(matches!(err, FerrotorchError::ShapeMismatch { .. }));
    }

    #[test]
    fn portable_matmul_rejects_inner_dim_mismatch() {
        let rt = runtime();
        let a = ferrotorch_core::from_vec(vec![1.0_f32; 6], &[2, 3]).unwrap();
        let b = ferrotorch_core::from_vec(vec![1.0_f32; 8], &[4, 2]).unwrap();
        let err = portable_matmul(&a, &b, &rt).unwrap_err();
        assert!(matches!(err, FerrotorchError::ShapeMismatch { .. }));
    }

    #[test]
    fn portable_add_rejects_shape_mismatch() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[1.0_f32, 2.0, 3.0]).unwrap();
        let b = ferrotorch_core::tensor(&[1.0_f32, 2.0]).unwrap();
        let err = portable_add(&a, &b, &rt).unwrap_err();
        assert!(matches!(err, FerrotorchError::ShapeMismatch { .. }));
    }

    #[test]
    fn portable_add_large_shape() {
        // Exercise multi-cube launch (more than 256 elements so we go past
        // one cube).
        let rt = runtime();
        let n: usize = 1024;
        let a: Vec<f32> = (0..n).map(|i| i as f32).collect();
        let b: Vec<f32> = (0..n).map(|i| (2 * i) as f32).collect();
        let ta = ferrotorch_core::from_vec(a.clone(), &[n]).unwrap();
        let tb = ferrotorch_core::from_vec(b.clone(), &[n]).unwrap();
        let tc = portable_add(&ta, &tb, &rt).unwrap();
        let data: &[f32] = tc.data().unwrap();
        for i in 0..n {
            assert_eq!(data[i], a[i] + b[i]);
        }
    }

    #[test]
    fn portable_matmul_square_8x8() {
        let rt = runtime();
        let n = 8usize;
        // identity matrix
        let mut a = vec![0.0_f32; n * n];
        for i in 0..n {
            a[i * n + i] = 1.0;
        }
        // arbitrary matrix
        let b: Vec<f32> = (0..n * n).map(|i| i as f32).collect();

        let ta = ferrotorch_core::from_vec(a, &[n, n]).unwrap();
        let tb = ferrotorch_core::from_vec(b.clone(), &[n, n]).unwrap();
        let c = portable_matmul(&ta, &tb, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        assert_eq!(data, b.as_slice(), "I * B should equal B");
    }

    // Helper: approximate-equal for float comparisons in transcendental tests.
    fn assert_close(actual: &[f32], expected: &[f32], tol: f32) {
        assert_eq!(actual.len(), expected.len());
        for (i, (a, e)) in actual.iter().zip(expected.iter()).enumerate() {
            assert!(
                (a - e).abs() < tol,
                "at index {i}: expected {e}, got {a} (tol={tol})"
            );
        }
    }

    #[test]
    fn portable_div_runs_on_gpu() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[10.0_f32, 20.0, 30.0, 40.0]).unwrap();
        let b = ferrotorch_core::tensor(&[2.0_f32, 4.0, 5.0, 8.0]).unwrap();
        let c = portable_div(&a, &b, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        assert_close(data, &[5.0, 5.0, 6.0, 5.0], 1e-4);
    }

    #[test]
    fn portable_neg_runs_on_gpu() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[-3.0_f32, -1.0, 0.0, 1.0, 3.0]).unwrap();
        let c = portable_neg(&a, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        assert_close(data, &[3.0, 1.0, 0.0, -1.0, -3.0], 1e-6);
    }

    #[test]
    fn portable_abs_runs_on_gpu() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[-3.0_f32, -1.0, 0.0, 1.0, 3.0]).unwrap();
        let c = portable_abs(&a, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        assert_close(data, &[3.0, 1.0, 0.0, 1.0, 3.0], 1e-6);
    }

    #[test]
    fn portable_exp_runs_on_gpu() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[0.0_f32, 1.0, 2.0, -1.0]).unwrap();
        let c = portable_exp(&a, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        let expected: Vec<f32> = [0.0, 1.0, 2.0, -1.0].iter().map(|x: &f32| x.exp()).collect();
        assert_close(data, &expected, 1e-3);
    }

    #[test]
    fn portable_ln_runs_on_gpu() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[1.0_f32, std::f32::consts::E, 10.0, 100.0]).unwrap();
        let c = portable_ln(&a, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        let expected: Vec<f32> = [1.0_f32, std::f32::consts::E, 10.0, 100.0]
            .iter()
            .map(|x| x.ln())
            .collect();
        assert_close(data, &expected, 1e-3);
    }

    #[test]
    fn portable_sqrt_runs_on_gpu() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[0.0_f32, 1.0, 4.0, 9.0, 16.0]).unwrap();
        let c = portable_sqrt(&a, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        assert_close(data, &[0.0, 1.0, 2.0, 3.0, 4.0], 1e-4);
    }

    #[test]
    fn portable_sin_runs_on_gpu() {
        let rt = runtime();
        let pi = std::f32::consts::PI;
        let a = ferrotorch_core::tensor(&[0.0_f32, pi / 2.0, pi, 3.0 * pi / 2.0]).unwrap();
        let c = portable_sin(&a, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        assert_close(data, &[0.0, 1.0, 0.0, -1.0], 1e-3);
    }

    #[test]
    fn portable_cos_runs_on_gpu() {
        let rt = runtime();
        let pi = std::f32::consts::PI;
        let a = ferrotorch_core::tensor(&[0.0_f32, pi / 2.0, pi, 3.0 * pi / 2.0]).unwrap();
        let c = portable_cos(&a, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        assert_close(data, &[1.0, 0.0, -1.0, 0.0], 1e-3);
    }

    #[test]
    fn portable_tanh_runs_on_gpu() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[-2.0_f32, -0.5, 0.0, 0.5, 2.0]).unwrap();
        let c = portable_tanh(&a, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        let expected: Vec<f32> = [-2.0_f32, -0.5, 0.0, 0.5, 2.0]
            .iter()
            .map(|x| x.tanh())
            .collect();
        assert_close(data, &expected, 1e-4);
    }

    #[test]
    fn portable_sigmoid_runs_on_gpu() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[-4.0_f32, -1.0, 0.0, 1.0, 4.0]).unwrap();
        let c = portable_sigmoid(&a, &rt).unwrap();
        let data: &[f32] = c.data().unwrap();
        let expected: Vec<f32> = [-4.0_f32, -1.0, 0.0, 1.0, 4.0]
            .iter()
            .map(|x| 1.0 / (1.0 + (-x).exp()))
            .collect();
        assert_close(data, &expected, 1e-4);
    }

    #[test]
    fn portable_sigmoid_large_shape() {
        // Sigmoid across multiple cubes + verify numerical stability.
        let rt = runtime();
        let n: usize = 1024;
        let input: Vec<f32> = (0..n).map(|i| (i as f32 - 512.0) * 0.01).collect();
        let t = ferrotorch_core::from_vec(input.clone(), &[n]).unwrap();
        let out = portable_sigmoid(&t, &rt).unwrap();
        let data: &[f32] = out.data().unwrap();
        for (i, &x) in input.iter().enumerate() {
            let expected = 1.0 / (1.0 + (-x).exp());
            assert!(
                (data[i] - expected).abs() < 1e-4,
                "sigmoid mismatch at {i}: got {}, expected {}",
                data[i],
                expected
            );
        }
    }

    #[test]
    fn portable_exp_then_ln_is_identity() {
        // End-to-end check: ln(exp(x)) ≈ x.
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[-2.0_f32, -0.5, 0.1, 1.0, 3.0]).unwrap();
        let e = portable_exp(&a, &rt).unwrap();
        let back = portable_ln(&e, &rt).unwrap();
        let data: &[f32] = back.data().unwrap();
        assert_close(data, &[-2.0, -0.5, 0.1, 1.0, 3.0], 1e-3);
    }

    #[test]
    fn portable_div_rejects_shape_mismatch() {
        let rt = runtime();
        let a = ferrotorch_core::tensor(&[1.0_f32, 2.0, 3.0]).unwrap();
        let b = ferrotorch_core::tensor(&[1.0_f32, 2.0]).unwrap();
        let err = portable_div(&a, &b, &rt).unwrap_err();
        assert!(matches!(err, FerrotorchError::ShapeMismatch { .. }));
    }
}

// ---------------------------------------------------------------------------
// Tests that run on every build (no backend feature needed)
// ---------------------------------------------------------------------------

#[cfg(all(test, not(any(feature = "wgpu", feature = "cuda", feature = "rocm"))))]
mod no_backend_tests {
    use super::*;
    use crate::runtime::CubeDevice;

    #[test]
    fn runtime_construction_errors_without_backend() {
        let err = CubeRuntime::new(CubeDevice::Wgpu(0)).unwrap_err();
        assert!(matches!(err, FerrotorchError::DeviceUnavailable));
    }
}