swaitsandClaude Opus 4.6
3102fc747a
Implement full SSD1306 OLED display support: - Splash screen on boot (1.5s) with project name, version, board - Dashboard showing radio state, config, counters, RSSI/SNR - RSSI history sparkline (64-sample ring buffer, 2px-wide bars) - DisplayOn/DisplayOff host commands routed via dedicated channel - Pure render functions against generic DrawTarget (no hardware coupling) - Display on/off control bypasses radio task entirely Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
122 lines
3.2 KiB
Rust
122 lines
3.2 KiB
Rust
//! Exp approximation for a single-precision float.
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//!
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//! Method described at: <https://stackoverflow.com/a/6985769/2036035>
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use super::{EXPONENT_BIAS, F32};
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use core::f32::consts;
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impl F32 {
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/// Returns `e^(self)`, (the exponential function).
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#[inline]
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pub fn exp(self) -> Self {
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self.exp_ln2_approx(4)
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}
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/// Exp approximation for `f32`.
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pub(crate) fn exp_ln2_approx(self, partial_iter: u32) -> Self {
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if self == Self::ZERO {
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return Self::ONE;
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}
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if (self - Self::ONE).abs() < f32::EPSILON {
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return consts::E.into();
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}
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if (self - (-Self::ONE)).abs() < f32::EPSILON {
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return Self::ONE / consts::E;
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}
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// log base 2(E) == 1/ln(2)
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// x_fract + x_whole = x/ln2_recip
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// ln2*(x_fract + x_whole) = x
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let x_ln2recip = self * consts::LOG2_E;
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let x_fract = x_ln2recip.fract();
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let x_trunc = x_ln2recip.trunc();
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//guaranteed to be 0 < x < 1.0
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let x_fract = x_fract * consts::LN_2;
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let fract_exp = x_fract.exp_smallx(partial_iter);
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//need the 2^n portion, we can just extract that from the whole number exp portion
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let fract_exponent: i32 = fract_exp
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.extract_exponent_value()
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.saturating_add(x_trunc.0 as i32);
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if fract_exponent < -(EXPONENT_BIAS as i32) {
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return Self::ZERO;
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}
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if fract_exponent > ((EXPONENT_BIAS + 1) as i32) {
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return Self::INFINITY;
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}
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fract_exp.set_exponent(fract_exponent)
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}
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/// if x is between 0.0 and 1.0, we can approximate it with the a series
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///
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/// Series from here:
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/// <https://stackoverflow.com/a/6984495>
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///
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/// e^x ~= 1 + x(1 + x/2(1 + (x?
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#[inline]
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pub(crate) fn exp_smallx(self, iter: u32) -> Self {
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let mut total = 1.0;
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for i in (1..=iter).rev() {
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total = 1.0 + ((self.0 / (i as f32)) * total);
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}
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Self(total)
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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::F32;
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pub(crate) const MAX_ERROR: f32 = 0.001;
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/// exp test vectors - `(input, output)`
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pub(crate) const TEST_VECTORS: &[(f32, f32)] = &[
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(1e-07, 1.0000001),
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(1e-06, 1.000001),
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(1e-05, 1.00001),
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(1e-04, 1.0001),
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(0.001, 1.0010005),
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(0.01, 1.0100502),
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(0.1, 1.105171),
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(1.0, 2.7182817),
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(10.0, 22026.465),
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(-1e-08, 1.0),
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(-1e-07, 0.9999999),
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(-1e-06, 0.999999),
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(-1e-05, 0.99999),
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(-1e-04, 0.9999),
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(-0.001, 0.9990005),
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(-0.01, 0.99004984),
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(-0.1, 0.9048374),
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(-1.0, 0.36787945),
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(-10.0, 4.539_993e-5),
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];
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#[test]
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fn sanity_check() {
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assert_eq!(F32(-1000000.0).exp(), F32::ZERO);
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for &(x, expected) in TEST_VECTORS {
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let exp_x = F32(x).exp();
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let relative_error = (exp_x - expected).abs() / expected;
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assert!(
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relative_error <= MAX_ERROR,
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"relative_error {} too large for input {} : {} vs {}",
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relative_error,
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x,
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exp_x,
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expected
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);
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}
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}
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}
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