3.4.1. Signed Fractional Binary
<sign> <integer bits>.<fractional bits>
A signed binary fractional number is interpreted as shown below:
<sign> <x1 integer bits>.<y1 fractional bits> Original input data
<sign> <x2 integer bits>.<y2 fractional bits> Original coefficient data
<sign> <i integer bits>.<y1 + y2 fractional bits> Full precision after FIR calculation
<sign> <x3 integer bits>.<y3 fractional bits> Output data after limiting precision
where i = ceil(log2ceil(number of coefficients/interpolation factor)) + x1 + x2
For example, if the number has 3 fractional bits and 4 integer bits plus a sign bit, the entire 8-bit integer number is divided by 8, which gives a number with a binary fractional component.
The total number of bits equals to the sign bits + integer bits + fractional bits. The sign + integer bits is equal to Input Bit Width – Input Fractional Bit Width with a constraint that at least 1 bit must be specified for the sign.