okhdr 👌

31 29          19           9            0
+-+------------+------------+------------+
| |   b (10)   |   a (10)   |   L (10)   |
+-+------------+------------+------------+

// 10:10:10 Oklab packing (30 bits total)
// Layout: [ b:10 | a:10 | L:10 ]
//   can be stored e.g. in `rgb10a2uint` / `A2B10G10R10_UINT_PACK32` texture
// Ranges: L ∈ [0,2], a ∈ [-0.5,+0.5], b ∈ [-0.5,+0.5]
// Info: Encloses all of Rec. 2020, and HDR up to 8x reference white
//   (e.g. 1600 nits with D65 at 203 cd/m² from ITU-R BT.2408)

uint32_t pack( float L, float a, float b ) {
    uint32_t Lbits = (uint32_t)roundf( ( L / 2.0f ) * 1023.0f );            //  10 bits
    uint32_t abits = (uint32_t)roundf( ( ( a + 0.5f ) / 1.0f ) * 1023.0f ); //  10 bits
    uint32_t bbits = (uint32_t)roundf( ( ( b + 0.5f ) / 1.0f ) * 1023.0f ); //  10 bits
    return ( bbits << 20 ) | ( abits << 10 ) | Lbits;
}

void unpack( uint32_t p, float* L, float* a, float* b ) {
    uint32_t Lbits = p & 0x3FF;
    uint32_t abits = ( p >> 10 ) & 0x3FF;
    uint32_t bbits = ( p >> 20 ) & 0x3FF;
    *L = ( Lbits / 1023.0f ) * 2.0f;
    *a = ( abits / 1023.0f ) - 0.5f;
    *b = ( bbits / 1023.0f ) - 0.5f;
}