In the example above, we only specified the Word Length and Fractional Length of the fixed
point data types using data type expressions. However, for greater control over the
fixed point types in your design, you can also specify the Signedness, Rounding, and
Overflow. In general the format used for specifying fixed point data types using the
data type expression is
x_[u/s]fix[wl]_En[fl]_[r<round>w<overflow>]- u
- Unsigned
- s
- Signed
- wl
- Word length
- fl
- Fractional length
<round>: Specify the corresponding index from the following table.
This is optional. If not specified, the default value is 6 (Truncation to minus
infinity). Note that for the rounding cases (1 to 5), the data is rounded to the nearest
value that can be represented in the format. When there is a need for a tie breaker,
these particular roundings behave as specified in the Meaning column.
| Index | Meaning |
|---|---|
| 1 | Round to Plus Infinity |
| 2 | Round to Zero |
| 3 | Round to Minus Infinity |
| 4 | Round to Infinity |
| 5 | Convergent Rounding |
| 6 | Truncation to Minus Infinity |
| 7 | Truncation to Zero |
<overflow>: Specify the corresponding index from table below. It's
optional. If not specified, default value is 4 (Wrap around).
| Index | Meaning |
|---|---|
| 1 | Saturation |
| 2 | Saturation to Zero |
| 3 | Symmetrical Saturation |
| 4 | Wrap Around |
| 5 | Sign-Magnitude Wrap Around |
Example: x_ufix8_En6_r6w4 represents a fixed
point data type with:
- Signedness
- Unsigned
- Word Length
- 8
- Fractional Length
- 6
- Rounding Mode
- Truncation to Minus Infinity
- Overflow Mode
- Wrap Around