getid3_ac3::heavyCompression( int $compre ): float|int

664	public static function heavyCompression($compre) {665		// The first four bits indicate gain changes in 6.02dB increments which can be666		// implemented with an arithmetic shift operation. The following four bits667		// indicate linear gain changes, and require a 5-bit multiply.668		// We will represent the two 4-bit fields of compr as follows:669		//   X0 X1 X2 X3 . Y4 Y5 Y6 Y7670		// The meaning of the X values is most simply described by considering X to represent a 4-bit671		// signed integer with values from -8 to +7. The gain indicated by X is then (X + 1) * 6.02 dB. The672		// following table shows this in detail.673 674		// Meaning of 4 msb of compr675		//  7    +48.16 dB676		//  6    +42.14 dB677		//  5    +36.12 dB678		//  4    +30.10 dB679		//  3    +24.08 dB680		//  2    +18.06 dB681		//  1    +12.04 dB682		//  0     +6.02 dB683		// -1         0 dB684		// -2     -6.02 dB685		// -3    -12.04 dB686		// -4    -18.06 dB687		// -5    -24.08 dB688		// -6    -30.10 dB689		// -7    -36.12 dB690		// -8    -42.14 dB691 692		$fourbit = str_pad(decbin(($compre & 0xF0) >> 4), 4, '0', STR_PAD_LEFT);693		if ($fourbit[0] == '1') {694			$log_gain = -8 + bindec(substr($fourbit, 1));695		} else {696			$log_gain = bindec(substr($fourbit, 1));697		}698		$log_gain = ($log_gain + 1) * getid3_lib::RGADamplitude2dB(2);699 700		// The value of Y is a linear representation of a gain change of up to -6 dB. Y is considered to701		// be an unsigned fractional integer, with a leading value of 1, or: 0.1 Y4 Y5 Y6 Y7 (base 2). Y can702		// represent values between 0.111112 (or 31/32) and 0.100002 (or 1/2). Thus, Y can represent gain703		// changes from -0.28 dB to -6.02 dB.704 705		$lin_gain = (16 + ($compre & 0x0F)) / 32;706 707		// The combination of X and Y values allows compr to indicate gain changes from708		//  48.16 - 0.28 = +47.89 dB, to709		// -42.14 - 6.02 = -48.16 dB.710 711		return $log_gain - $lin_gain;712	}
PHP	Compiled	Executed	Branches	Notes
8.6-dev	36	30–32	1
8.5	36	30–32	1
8.4	36	30–32	1	6 fewer instructions than PHP 8.3
8.3	42	33–35	1
8.2	42	33–35	1
8.1	42	33–35	1
7.4	42	33–35	1