Perform one-dimensional lookup operation with an input index.
Library
Lookup Tables
Description
The Lookup Table block implements a simple read-only memory block with an
input index. The block maps input to an output value by looking up a table of values you define
with a Table data parameter.
The input value is used as a zero-based index into the table data. The
Input bias parameter is an offset to the index value (to support negative
indexing). A When input is out of range parameter lets you specify the behavior
of the block if the index value exceeds the valid table size range.
In the example above, the Table data setting for the Lookup
Table block is [7 3 4 8 9 4 1 5] with an input bias of 1.
Data Type Support
The Lookup Table block accepts the following data types to represent scalar index value: int8, uint8, int16, uint16, int32, uint32, and fixed-point type. Fixed-point inputs is shifted appropriately to generate an integer index.
The output data type is same as the Table data parameter
type. Inputs for indexing must be real, but table data can be complex.
Parameters
- Table Data
-
This parameter accepts a 1-D vector of table values. The size of the vector determines the valid index range for the input index. The data will be explicitly converted into the type specified in the
Output data typeparameter. If the input index exceeds table size andSaturate at table endsis specified for theWhen input is out of rangeparameter, then index value is saturated to either top or bottom of table size range. IfWrap aroundis specified for theWhen input is out of rangeparameter, the index is wrapped into the valid table size range.Note: Large tables should be defined via a Simulink workspace variable due to space limitations in the block dialog box. - Input bias
- This parameter is an offset into the table data that will be added to the index input. This makes it possible to use negative indices and perform look up operation.
- When input is out of range
- This parameter will guard the index value if it exceeds the valid table size range.
Following are the settings for the
When input is out of rangeparameter.Table 1. When Input Is Out of Range Parameter Setting Description Saturate at table ends If index value exceeds the valid table size range, then index value is saturated to either top or bottom of table size range, depending on the overflow direction. Wrap around If index value exceeds the valid table size range, then index value is wrapped into the valid table size range. - Output data type
- Specifies the output data type.
Following are settings for the
Output data typeparameter.Table 2. Output Data Type Parameter Setting Description double double precision floating-point single single precision floating-point int8 8-bit signed integer uint8 8-bit unsigned integer int16 16-bit signed integer uint16 16-bit unsigned integer int32 32-bit signed integer uint32 32-bit unsigned integer boolean boolean fixed fixed-point half half precision floating-point data type expression A string that specifies the output data type. See "Working with Data Type Expression" in the Vitis Model Composer User Guide (UG1483).