Building a 32-bit float out of its 4 composite bytes

by

You could use a memcpy (Result)

float f;
uchar b[] = {b3, b2, b1, b0};
memcpy(&f, &b, sizeof(f));
return f;

or a union* (Result)

union {
  float f;
  uchar b[4];
} u;
u.b[3] = b0;
u.b[2] = b1;
u.b[1] = b2;
u.b[0] = b3;
return u.f;

But this is no more portable than your code, since there is no guarantee that the platform is little-endian or the float is using IEEE binary32 or even sizeof(float) == 4.

(Note*: As explained by @James, it is technically not allowed in the standard (C++ ยง[class.union]/1) to access the union member u.f.)

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