//! MACROGROK fixed-point INFER4 — Rust port of MACROGROK/src/sim.py + examples/infer4.asm
//! Q1.14 (16384 per 1.0), Q3.12 (4096 per 1.0), Q7.24 ACC, saturate.

const WEIGHTS_Q1_14: [i16; 4] = [2458, -1638, 819, 3277];
const BIAS_Q3_12: i32 = -256;
const FLAG_VALID: u16 = 0x1;
const FLAG_SAT: u16 = 0x2;
const FLAG_POSITIVE: u16 = 0x4;

#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub struct Q1_14(pub i16);

pub fn infer4(input: [Q1_14; 4]) -> (i16, i32, u16) {
    // DOT4 Q1.14*Q1.14>>4 accum Q3.24
    let mut acc: i32 = 0;
    for (w, inp) in WEIGHTS_Q1_14.iter().zip(input.iter()) {
        let prod = (*w as i32) * (inp.0 as i32); // Q2.28
        acc = acc.wrapping_add(prod >> 4);
    }
    let mut tmp0 = acc >> 12; // Q3.12
    tmp0 += BIAS_Q3_12;
    let mut flags: u16 = 0;
    let mut sat = false;
    if tmp0 < -8192 { tmp0 = -8192; sat = true; }
    if tmp0 > 8191 { tmp0 = 8191; sat = true; }
    if tmp0 >= 0 { flags |= FLAG_POSITIVE; }
    if sat { flags |= FLAG_SAT; }
    let tmp1: i16 = if tmp0 >= 0 { 16384u16 as i16 } else { -16384 }; // +1.0 / -1.0 Q1.14
    // Persistent STATE (Q1.14 scale) — 3/4 low-pass
    use std::sync::Mutex;
    static STATE: Mutex<i16> = Mutex::new(0);
    let mut state = STATE.lock().unwrap();
    *state = ((3 * (*state as i32) + tmp1 as i32) / 4) as i16;
    let out = *state;
    flags |= FLAG_VALID;
    (out, tmp0, flags)
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn test_infer4_basic() {
        let (out, _, _) = infer4([Q1_14(16384), Q1_14(0), Q1_14(0), Q1_14(0)]);
        assert!(out != 0);
    }
}