Nonlinear operation method suitable for audio encoding/decoding and hardware applying the same

A nonlinear operation method suitable for audio decoding, existing in an inverse quantization process for audio decoding, the nonlinear operation equation is f (X)=X4/3, wherein X represents an inverse package data, and the nonlinear operation method suitable for audio decoding comprising:

• building up a query table, the query table comprising a plurality of inverse package data X and a plurality of corresponding values f(X) that correspond to the inverse package data X, wherein the query table is represented as a function T(X), and T(X)=X4/3, 1≦X≦S, where S represents a data range included in the query table;
• analyzing and providing a modified error quantity function fa(z) represented by a power of 2 equation, wherein let
• 55 z = ⌊ X 8 n ⌋ ,
• n=1 or 2 to have z fall in the data range S of the query table;
• wherein when the inverse package data X that is intended to query is greater than the data range S, the values of T(z) and T(z+1) are obtained from the query table and are defined as Y1 and Y2, respectively, where z and (z+1) fall in the data range S of the query table, respectively;
• and
• calculating a corresponding value f(X) of any one of the inverse package data X that is beyond the data range S by using a two-phase interpolation method, comprising the steps of:
• multiplying Y1 and Y2 by a recover coefficient to obtain a corresponding value of X1 and X2, i.e. f(X1) and f(X2), respectively;
• generating a secant equation that passes through two points of f(X1) and f(X2);
• eliminating a maximum error quantity in an [X1, X2] interval via the modified error quantity function fa(z) according to the secant equation, so as to divide a range from f(X1) to f(X2) into two segments, and to obtain a value of f(X3) that has a minimum error;
• obtaining a corresponding value f(X) of any one of the inverse package data X in an [X1, X3] interval via the interpolation method;
• and
• obtaining a corresponding value f(X) of any one of the inverse package data X in an [X3, X2] interval via the interpolation method.

An applied hardware of a nonlinear operation suitable for audio encoding/decoding, the applied hardware existing in a MPEG integrated circuit is used to solve a nonlinear operation equation needed in a quantization/inverse quantization process, and the applied hardware of the nonlinear operation suitable for audio encoding/decoding comprising:

• a shifter, receiving a sampling data X, obtaining an operation sampling data z after applying a right-shift operation to have the operation sampling data z fall in a data range S;
• a read only memory, storing a query table that includes the data range S, wherein the query table is represented as a function T(X), the read only memory outputs a value of T(z) and T(z+1) after receiving the operation sampling data z and defining them as Y1 and Y2, respectively, where z and (z+1) fall in the data range S of the query table, respectively;
• a difference calculator, coupled to the read only memory, receiving Y1 and Y2 to obtain a difference of (Y2−Y1), and applying a power of 2 operation onto the difference to output an original difference;
• a modified error quantity function generator, coupled to the shifter, receiving the operation sampling data z, and obtaining a modified error quantity function fa(z) after applying a subtraction and shift operation;
• and
• an interpolation method calculator, receiving the original difference and the modified error quantity function fa(z), and performing a summation/subtraction operation, a selection process, a coefficient multiply operation, and a shift operation to obtain a nonlinear operation corresponding value of the sampling data X.