### C code, for when subtracting two floats, checking for "might as well treat as zero"

/* detecting total precision loss when subtracting two floats */

/* if exponent of the larger of A and B,

minus the exponent of the difference of A and B

is greater than the number of digits of the mantessa,

it's now basically zero, all information lost, that is,

it is smaller than the smallest number representable

by a normalized float with an exponent the same as

the larger of A and B */

int istoosmalldiff_f (float a, float b)

{

float m_frac, d_frac;

int m_exp, d_exp;

m_frac= frexpf(fmaxf(a, b), &m_exp);

d_frac= frexpf((a - b), &d_exp);

/* my libc doesnt define FLT_MANT_DIG, foo! */

/* just hardwire 24 for floats */

return ((d_exp - m_exp) >= (24-1));

}

Did I get this right?