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Altera_Forum's avatar
Altera_Forum
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16 years ago

Combine 4 bytes in float

Hi all!

i'm receiving a float (32bit) from the serial port...

i receive the correct sequence but now i'm trying to recombine the number with this code:

unsigned char b1,b2,b3,b4;

b1=GetUart();

b2=GetUart();

b3=GetUart();

b4=GetUart();

coeff = (float)((b4&0xFF) | ((b3<<8)&0xFF00) | ((b2<<16)&0xFF0000) | ((b1<<24)&0xFF000000));

i'm sending pigreco (for example) and receive the bytes: 0xdb,0x0f,0x49,0x40 that is the correct value, just swap.

but if i print the value result coeff :3.675212e+09

any idea??

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    You need to cast the pointer, not the value try:

    union { unsigned char b[4]; float f; } x;

    x.b[0] = GetUart(); ...

    coeff = x.f;
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    thanks!

    i've never userd this function "union"

    by the way, the compiler say me:

    ../acquisition_6.c:78: error: `b' undeclared (first use in this function)

    ../acquisition_6.c:78: error: (Each undeclared identifier is reported only once

    ../acquisition_6.c:78: error: for each function it appears in.)

    ../acquisition_6.c:83: error: incompatible type for argument 1 of `printf'

    but the code is:

    --- Quote Start ---

    void ParseCoeff(){

    [...]

    union { unsigned char b[4]; float f; } x;

    if (UartHasFourByte()){

    b[1] = GetUart();

    b[2] = GetUart();

    b[3] = GetUart();

    b[4] = GetUart();

    coeff = x.f;

    [...]

    --- Quote End ---