fixed.hpp

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// sbl/dsp/fixed.hpp — Fixed-point constants for the DSP layer
//
// Q16 conventions used throughout sbl::dsp:
//   - Phase: uint32_t full range [0, 2^32) = one cycle
//   - Normalized uint16_t: 0 = 0.0, 65535 = ~1.0
//   - Fractional mask: lower 16 bits after index extraction
 
#pragma once
 
#include <cstdint>
 
namespace sbl::dsp {
 
// Q16 fixed-point: 1.0 represented as 65536 (one past uint16_t range)
inline constexpr uint32_t Q16_ONE = 65536u;
 
// Maximum uint16_t value — end of normalized [0, 65535] range
inline constexpr uint16_t U16_MAX = 65535u;
 
// Midpoint of uint16_t range — "linear" / center value for curve parameter
inline constexpr uint16_t U16_MID = 32768u;
 
// 16-bit fractional mask for phase extraction
inline constexpr uint16_t FRAC16_MASK = 0xffff;
 
// 24-bit audio sample range (matches SAI/I2S int32 format)
inline constexpr int32_t SAMPLE_MAX_24 =  8388607;   // 2^23 - 1
inline constexpr int32_t SAMPLE_MIN_24 = -8388607;   // -(2^23 - 1), symmetric
 
/// Clamp value to 24-bit audio range
inline constexpr int32_t saturate_24(int32_t x) {
    return (x > SAMPLE_MAX_24) ? SAMPLE_MAX_24
         : (x < SAMPLE_MIN_24) ? SAMPLE_MIN_24
         : x;
}
 
} // namespace sbl::dsp