Intel® High Level Synthesis Compiler Standard Edition: Best Practices Guide

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ID 683259
Date 12/18/2019
Public
Document Table of Contents
Document Table of Contents x
1. Intel® HLS Compiler Standard Edition Best Practices Guide 2. Best Practices for Coding and Compiling Your Component 3. Interface Best Practices 4. Loop Best Practices 5. Memory Architecture Best Practices 6. Datatype Best Practices 7. Advanced Troubleshooting A. Intel® HLS Compiler Standard Edition Best Practices Guide Archives B. Document Revision History for Intel® HLS Compiler Standard Edition Best Practices Guide
3. Interface Best Practices x
3.1. Choose the Right Interface for Your Component 3.2. Avoid Pointer Aliasing
3.1. Choose the Right Interface for Your Component x
3.1.1. Pointer Interfaces 3.1.2. Avalon® Memory Mapped Master Interfaces 3.1.3. Avalon® Memory Mapped Slave Interfaces 3.1.4. Avalon® Streaming Interfaces 3.1.5. Pass-by-Value Interface
4. Loop Best Practices x
4.1. Reuse Hardware By Calling It In a Loop 4.2. Parallelize Loops 4.3. Construct Well-Formed Loops 4.4. Minimize Loop-Carried Dependencies 4.5. Avoid Complex Loop-Exit Conditions 4.6. Convert Nested Loops into a Single Loop 4.7. Declare Variables in the Deepest Scope Possible
4.2. Parallelize Loops x
4.2.1. Pipeline Loops 4.2.2. Unroll Loops 4.2.3. Example: Loop Pipelining and Unrolling
5. Memory Architecture Best Practices x
5.1. Example: Overriding a Coalesced Memory Architecture 5.2. Example: Overriding a Banked Memory Architecture 5.3. Merge Memories to Reduce Area 5.4. Example: Specifying Bank-Selection Bits for Local Memory Addresses
5.3. Merge Memories to Reduce Area x
5.3.1. Example: Merging Memories Depth-Wise 5.3.2. Example: Merging Memories Width-Wise
6. Datatype Best Practices x
6.1. Avoid Implicit Data Type Conversions 6.2. Avoid Negative Bit Shifts When Using the ac_int Datatype
7. Advanced Troubleshooting x
7.1. Component Fails Only In Cosimulation 7.2. Component Gets Bad Quality of Results
1. Intel® HLS Compiler Standard Edition Best Practices Guide
2. Best Practices for Coding and Compiling Your Component
3. Interface Best Practices
4. Loop Best Practices
5. Memory Architecture Best Practices
6. Datatype Best Practices
7. Advanced Troubleshooting
A. Intel® HLS Compiler Standard Edition Best Practices Guide Archives
B. Document Revision History for Intel® HLS Compiler Standard Edition Best Practices Guide

6.2. Avoid Negative Bit Shifts When Using the ac_int Datatype

The ac_int datatype differs from other languages, including C and Verilog, in bit shifting. By default, if the shift amount is of a signed datatype ac_int allows negative shifts.

In hardware, this negative shift results in the implementation of both a left shifter and a right shifter. The following code example shows a shift amount that is a signed datatype. 

int14 shift_left(int14 a, int14 b) {
    return (a << b);
}

If you know that the shift is always in one direction, to implement an efficient shift operator, declare the shift amount as an unsigned datatype as follows: 

int14 efficient_left_only_shift(int14 a, uint14 b) {
    return (a << b);
}
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