PA-RISC Floating-Point Registers
The PA-RISC has 32 floating-point registers. The first four are used for status and exception registers. The rest can be addressed as 64-bit doubles, as two 32-bit floats in the right and left sides of the register, or even-odd pairs of registers as 128-bit extended floats.
| Register |
Description |
Data Type |
Edit |
Dive |
Specify in Expression |
| status |
Status register |
<int> |
no |
no |
$status |
| er1-er7 |
Exception registers |
<int> |
no |
no |
$er1-$er7 |
| fr4-fr31 |
Double floating-point registers |
<double> |
yes |
yes |
$fr4-$fr31 |
| fr4l-fr31l |
Left half floating-point registers |
<float> |
yes |
yes |
$fr4l-$fr31l |
| fr4r-fr31r |
Right half floating-point registers |
<float> |
yes |
yes |
$fr4r-$fr31r |
| fr4/fr5-fr30/fr31 |
Extended floating-point register pairs |
<extended> |
yes |
yes |
$fr4_fr5-$fr30_fr31 |
The floating-point status word controls the arithmetic rounding mode, enables user-level traps, enables floating-point exceptions, and indicates the results of comparisons.
| Type |
Value |
Meaning |
| Rounding Mode |
0 |
Round to nearest |
|
|
1 |
Round toward zero |
|
|
2 |
Round toward +infinity |
|
|
3 |
Round toward -infinity |
| Exception Enable and Exception Flag Bits |
V |
Invalid operation |
| Z |
Division by zero |
|
|
O |
Overflow |
|
|
U |
Underflow |
|
|
I |
Inexact result |
| Comparison Fields |
C |
Compare bit; contains the result of the most recent queued compare instruction. |
|
|
CQ |
Compare queue; contains the result of the second-most recent queued compare through the twelfth-most recent queued compare. Each queued compare instruction shifts the CQ field right one bit and copies the C bit into the left-most position. This field occupies the same bits as the CA field and is undefined after a targeted compare. |
|
|
CA |
Compare array; an array of seven compare bits, each of which contains the result of the most recent compare instruction targeting that bit. This field occupies the same bits as the CQ field and is undefined after a queued compare. |
| Other Flags: |
T |
Delayed trap |
|
|
D |
Denormalized as zero |
