import { clamp } from '../math/MathUtils.js';

// Fast Half Float Conversions, http://www.fox-toolkit.org/ftp/fasthalffloatconversion.pdf

const _tables = /*@__PURE__*/ _generateTables();

function _generateTables() {

	// float32 to float16 helpers

	const buffer = new ArrayBuffer( 4 );
	const floatView = new Float32Array( buffer );
	const uint32View = new Uint32Array( buffer );

	const baseTable = new Uint32Array( 512 );
	const shiftTable = new Uint32Array( 512 );

	for ( let i = 0; i < 256; ++ i ) {

		const e = i - 127;

		// very small number (0, -0)

		if ( e < - 27 ) {

			baseTable[ i ] = 0x0000;
			baseTable[ i | 0x100 ] = 0x8000;
			shiftTable[ i ] = 24;
			shiftTable[ i | 0x100 ] = 24;

			// small number (denorm)

		} else if ( e < - 14 ) {

			baseTable[ i ] = 0x0400 >> ( - e - 14 );
			baseTable[ i | 0x100 ] = ( 0x0400 >> ( - e - 14 ) ) | 0x8000;
			shiftTable[ i ] = - e - 1;
			shiftTable[ i | 0x100 ] = - e - 1;

			// normal number

		} else if ( e <= 15 ) {

			baseTable[ i ] = ( e + 15 ) << 10;
			baseTable[ i | 0x100 ] = ( ( e + 15 ) << 10 ) | 0x8000;
			shiftTable[ i ] = 13;
			shiftTable[ i | 0x100 ] = 13;

			// large number (Infinity, -Infinity)

		} else if ( e < 128 ) {

			baseTable[ i ] = 0x7c00;
			baseTable[ i | 0x100 ] = 0xfc00;
			shiftTable[ i ] = 24;
			shiftTable[ i | 0x100 ] = 24;

			// stay (NaN, Infinity, -Infinity)

		} else {

			baseTable[ i ] = 0x7c00;
			baseTable[ i | 0x100 ] = 0xfc00;
			shiftTable[ i ] = 13;
			shiftTable[ i | 0x100 ] = 13;

		}

	}

	// float16 to float32 helpers

	const mantissaTable = new Uint32Array( 2048 );
	const exponentTable = new Uint32Array( 64 );
	const offsetTable = new Uint32Array( 64 );

	for ( let i = 1; i < 1024; ++ i ) {

		let m = i << 13; // zero pad mantissa bits
		let e = 0; // zero exponent

		// normalized
		while ( ( m & 0x00800000 ) === 0 ) {

			m <<= 1;
			e -= 0x00800000; // decrement exponent

		}

		m &= ~ 0x00800000; // clear leading 1 bit
		e += 0x38800000; // adjust bias

		mantissaTable[ i ] = m | e;

	}

	for ( let i = 1024; i < 2048; ++ i ) {

		mantissaTable[ i ] = 0x38000000 + ( ( i - 1024 ) << 13 );

	}

	for ( let i = 1; i < 31; ++ i ) {

		exponentTable[ i ] = i << 23;

	}

	exponentTable[ 31 ] = 0x47800000;
	exponentTable[ 32 ] = 0x80000000;

	for ( let i = 33; i < 63; ++ i ) {

		exponentTable[ i ] = 0x80000000 + ( ( i - 32 ) << 23 );

	}

	exponentTable[ 63 ] = 0xc7800000;

	for ( let i = 1; i < 64; ++ i ) {

		if ( i !== 32 ) {

			offsetTable[ i ] = 1024;

		}

	}

	return {
		floatView: floatView,
		uint32View: uint32View,
		baseTable: baseTable,
		shiftTable: shiftTable,
		mantissaTable: mantissaTable,
		exponentTable: exponentTable,
		offsetTable: offsetTable
	};

}

// float32 to float16

function toHalfFloat( val ) {

	if ( Math.abs( val ) > 65504 ) console.warn( 'THREE.DataUtils.toHalfFloat(): Value out of range.' );

	val = clamp( val, - 65504, 65504 );

	_tables.floatView[ 0 ] = val;
	const f = _tables.uint32View[ 0 ];
	const e = ( f >> 23 ) & 0x1ff;
	return _tables.baseTable[ e ] + ( ( f & 0x007fffff ) >> _tables.shiftTable[ e ] );

}

// float16 to float32

function fromHalfFloat( val ) {

	const m = val >> 10;
	_tables.uint32View[ 0 ] = _tables.mantissaTable[ _tables.offsetTable[ m ] + ( val & 0x3ff ) ] + _tables.exponentTable[ m ];
	return _tables.floatView[ 0 ];

}

export {
	toHalfFloat,
	fromHalfFloat
};