# Re: Query on fmult in G.726

Started by April 30, 2002
 Hi all, I have a doubt in "FMULT" operation in G.726. The "fmult" is used to compute multiplication of fixed point number and a floating point number.In this function, the fixed point is first converted to floating point and the sign,magnitude and mantissas of both the floating point numbers are extracted. The resultant is computed as follows. WAnS = SRnS ** AnS ; signs of float1 float2 WAnEXP = SRnEXP + AnEXP ; exponents of float1 float2 WAnMANT = ((SRnMANT * AnMANT) + 48) >> 4 Mantissas of the two operands (Q6 format) are multiplied to form the product mantissa (Q12), which is then truncated in Q8 format.Thats why, we are right shifting the result by 4. But i dont understand why 48 is added to the product of mantissas. please clarify my doubt. Best regards, Prakash
Hi prakash ,
i believe the 48 is added for rounding the final prod. But like to have
more clarifications in depth.

vikram

-------Original Message-------

From: Bhanu Prakash
Date: Tuesday, April 30, 2002 21:18:30
To:
Subject: [speechcoding] Re: Query on fmult in G.726

Hi all,

I have a doubt in "FMULT" operation in G.726.
The "fmult" is used to compute multiplication of fixed point number and
a floating point number.In this function, the fixed point is first converted
to floating point and
the sign,magnitude and mantissas of both the floating point numbers are
extracted.

The resultant is computed as follows.

WAnS == SRnS ** AnS ; signs of float1 float2
WAnEXP == SRnEXP + AnEXP ; exponents of float1 float2
WAnMANT == ((SRnMANT * AnMANT) + 48) >> 4

Mantissas of the two operands (Q6 format) are multiplied to form the product
mantissa (Q12),
which is then truncated in Q8 format.Thats why, we are right shifting the
result by 4.
But i dont understand why 48 is added to the product of mantissas.

Best regards,
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