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The functions in this section perform miscellaneous but common operations that are awkward to express with C operators. On some processors these functions can use special machine instructions to perform these operations faster than the equivalent C code.
fmin
function returns the lesser of the two values x
and y. It is similar to the expression
((x) < (y) ? (x) : (y)) |
If an argument is NaN, the other argument is returned. If both arguments are NaN, NaN is returned.
fmax
function returns the greater of the two values x
and y.
If an argument is NaN, the other argument is returned. If both arguments are NaN, NaN is returned.
fdim
function returns the positive difference between
x and y. The positive difference is x -
y if x is greater than y, and 0 otherwise.
If x, y, or both are NaN, NaN is returned.
fma
function performs floating-point multiply-add. This is
the operation (x &middot; y) + z, but the
intermediate result is not rounded to the destination type. This can
sometimes improve the precision of a calculation.
This function was introduced because some processors have a special
instruction to perform multiply-add. The C compiler cannot use it
directly, because the expression `x*y + z' is defined to round the
intermediate result. fma
lets you choose when you want to round
only once.
On processors which do not implement multiply-add in hardware,
fma
can be very slow since it must avoid intermediate rounding.
`math.h' defines the symbols FP_FAST_FMA
,
FP_FAST_FMAF
, and FP_FAST_FMAL
when the corresponding
version of fma
is no slower than the expression `x*y + z'.
In the GNU C library, this always means the operation is implemented in
hardware.
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