Datasheet

Floating-point Support

To untrap the Inexact Result exception:

__ieee_status(FE_IEEE_MASK_INEXACT, 0);

To clear the Underflow sticky flag:

__ieee_status(FE_IEEE_UNDERFLOW, 0);

5.3.2 The __fp_status function

Previous versions of the ARM libraries implemented a function called

__fp_status

, that

manipulated a status word in the floating-point environment. ARM still supports this

function, for backwards compatibility. It is defined in

stdlib.h

__fp_status

has the following prototype:

unsigned int __fp_status(unsigned int mask, unsigned int flags);

The function modifies the writable parts of the status word according to the parameters,

and returns the previous value of the whole word.

The writable bits are modified by setting them to

new = (old & ~mask) ^ flags;

Four different operations can be performed on each bit of the status word, depending on

the corresponding bits in mask and flags (Table 5-6).

The layout of the status word as seen by

__fp_status

is shown in Figure 5-2.

Figure 5-2 Floating-point status word layout

Table 5-6 Status word bit modification

Bit of mask Bit of flags Effect

0 0 Leave alone

01Toggle

1 0 Set to 0

1 1 Set to 1

031 24 23 21 20 16 15 13 12 8 7 5 4

System ID Masks Sticky

FPA onlyR R R