66 lines
1.5 KiB
Rust
66 lines
1.5 KiB
Rust
/// Fixed-point arithmetic with configurable fractional bits.
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///
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/// All operations use i64 internally with i128 intermediates
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/// for multiply to avoid overflow. Shift-and-add only.
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#[derive(Debug, Clone, Copy)]
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pub struct FixedPoint {
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pub frac_bits: u8,
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}
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impl FixedPoint {
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pub fn new(frac_bits: u8) -> Self {
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Self { frac_bits }
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}
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#[inline]
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pub fn one(&self) -> i64 {
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1i64 << self.frac_bits
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}
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#[inline]
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pub fn from_f64(&self, val: f64) -> i64 {
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(val * (1i64 << self.frac_bits) as f64).round() as i64
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}
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#[inline]
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pub fn to_f64(&self, val: i64) -> f64 {
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val as f64 / (1i64 << self.frac_bits) as f64
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}
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#[inline]
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pub fn mul(&self, a: i64, b: i64) -> i64 {
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((a as i128 * b as i128) >> self.frac_bits) as i64
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}
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#[inline]
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pub fn div(&self, a: i64, b: i64) -> i64 {
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if b == 0 {
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return if a >= 0 { i64::MAX } else { i64::MIN };
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}
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(((a as i128) << self.frac_bits) / b as i128) as i64
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn mul_basic() {
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let fp = FixedPoint::new(16);
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let a = fp.from_f64(2.5);
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let b = fp.from_f64(4.0);
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let result = fp.to_f64(fp.mul(a, b));
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assert!((result - 10.0).abs() < 0.001);
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}
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#[test]
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fn div_basic() {
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let fp = FixedPoint::new(16);
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let a = fp.from_f64(10.0);
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let b = fp.from_f64(4.0);
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let result = fp.to_f64(fp.div(a, b));
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assert!((result - 2.5).abs() < 0.001);
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}
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}
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