Find Pattern

ROHD-HCL comes with a FindPattern. The detailed API docs are available here.

A FindPattern will search for first/nth occurrence of a fixed-width pattern within a given Logic bus.

It takes a Binary Logic bus and finds the position of the desired pattern within the bus. A FindPattern function without any constructor arguments will find the first pattern from the start of the bus. That is to say, by default a FindPattern will go for finding the first occurrence when no n is passed. In addition, with fromStart which is set as true by default to search for the pattern from the start of the bus. Both boolean fromStart and Logic n are optional. Logic bus and Logic pattern are mandatory argument.

FindPattern has an output pin named as index, for the index position on the occurrence searched taken from the LSB (Least Significant Bit) or MSB (Most Significant Bit) depending on the search direction defined with boolean fromStart.

Implementation

To find the index of a fixed-width pattern in a bus. By default, it will find the first occurrence of the pattern from the start of the bus. The search direction is defined by fromStart argument. To find index of the second or third occurrence, define the n value to the desired number of occurrences.

index and n is zero-based index, where first index and first occurrence is defined 0.

If pattern is not found in the bus, output index will be 0, and if generateError is true, output error will be generated and is equal to 1.

Find Pattern from Start/End

To find the index of the first occurrence of specific pattern in a bus from start/end.

Find Pattern from Start

To get the index location of the pattern from start of the bus, simply pass the Logic bus and pattern. Ensure that the pattern width is smaller than the bus width. By default, it will find the first occurrence of the pattern from start of the bus.

For example, if bus is 10100001 and pattern is 1010, the output index will return 4 as the first occurrence of the pattern is found at the 5th-bit of the bus from the LSB.

final bus = Const(bin('10100001'), width: 8);
final pattern = Const(bin('1010'), width: 4);
final findPattern = FindPattern(bus, pattern);
expect(findPattern.index.value.toInt(), equals(4));

Find Pattern from End

To get the index location of the pattern from end of the bus (MSB), pass the Logic bus, Logic pattern and set the fromStart to false. Ensure that the pattern width is smaller than the bus width. By default, it will find the first occurrence of the pattern from end of the bus.

For example, if bus is 11101010 and pattern is 11101, the output index will return 0 as the first occurrence of the pattern is found at the 0th-bit of the bus from the MSB.

final bus = Const(bin('11101010'), width: 8);
final pattern = Const(bin('11101'), width: 5);
final findPattern = FindPattern(bus, pattern, fromStart: false);
expect(findPattern.index.value.toInt(), equals(0));

Find Nth Pattern from Start/End

To find the index of nth occurrence of specific pattern in a bus from start/end.

Find Nth Pattern from Start

To get the index location of the nth occurrence of pattern in the bus, simply pass the Logic bus and pattern and additional input Logic of n. By default n is null and will be set to 0 if it is not defined. n is zero-based indexing, so if you want to find the 2nd occurrence of the pattern, n should be set to 1.

For example, if bus is 10101001 and you want to find the 3rd occurrence of pattern of 01, pass input n as 2. The output index will return 5 as the 3rd occurrence of the pattern is found at the 5th-bit of the bus from the LSB.

final bus = Const(bin('10101001'), width: 8);
final pattern = Const(bin('01'), width: 2);
final n = Const(2, width: log2Ceil(bus.width) + 1);
final findPattern = FindPattern(bus, pattern, n: n);
expect(findPattern.index.value.toInt(), equals(5));

Find Nth Pattern from End

To get the index location of the nth occurrence of pattern from end of the bus (MSB), pass the Logic bus, Logic pattern, set fromStart to false with additional input Logic of n. By default n is null and will be set to 0 if it is not defined. n is zero-based indexing, so if you want to find the 2nd occurrence of the pattern, n should be set to 1.

For example, if bus is 10101001 and you want to find the 3rd occurrence of pattern of 01, pass input n as 2. The output index will return 6 as the 3rd occurrence of the pattern is found at the 6th-bit of the bus from the MSB.

final bus = Const(bin('10101001'), width: 8);
final pattern = Const(bin('01'), width: 2);
final n = Const(2, width: log2Ceil(bus.width) + 1);
final findPattern = FindPattern(bus, pattern, fromStart: false, n: n);
expect(findPattern.index.value.toInt(), equals(6));

Pattern not Found in Bus

If pattern is not found in the Logic bus, output index will be 0. To generate the output pin error, set the generateError boolean to true. By default, generateError is false. If pattern is not found, error will be 1.

final bus = Const(bin('00000000'), width: 8);
final pattern = Const(bin('111'), width: 3);
final findPattern = FindPattern(bus, pattern, generateError: true);
expect(findPattern.error!.value.toInt(), equals(1));