PM0014 datasheet(33/46 Pages) STMICROELECTRONICS

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PM0014

Arithmetic library functions

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5.7

Function approximation

5.7.1

sqrt_p16q16_p8q8

void sqrt_p16q16_p8q8 (short xmsb, short xlsb, short *Output).

Description:

The square root function is approximated by the Hoerner

polynomial. The input is in 16.16 format and the output is in 8.8

format with a precision to within three least significant bits.

Argument:

xmsb

Input most significant bits.

xlsb

Input least significant bits.

Output

Output pointer.

Algorithm:

x1/2

≈ 0.2075806 + 1.454895x - 1.34491x2 +1.106812x3 -

0.536499x4 + 0.11212116x5

Note:

The input value can range from 0 to 215 - 1/215.

In fact the previous approximation is valid only between 0.5 and 1

but all inputs are scaled into this range.

Assembly source

code:

sqrt_p16q16_p8q8.asm

Code size and cycles: Size: 330 bytes

Instruction cycles: 164

Test:

Two files are provided to test the function: an input vector file

(sqrt_p16q16_p8q8.in) and an output vector file

(sqrt_p16q16_p8q8.res):

sqrt_p16q16_p8q8.in is made as follows:

OpLsb1,

OpMsb1,

OpLsb2,

OpMsb2,

...

sqrt_p16q16_p8q8.res is made as follows:

Output1,

Output2,

...

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