---
id: "a9d80b9a-ac18-4643-bb6d-e082da651f2f"
name: freertos-64bit-division-implementation-14eb415121c6
description: "Implements 64-bit division functions (div_u64, div_s64, div64_u64, div64_s64) for FreeRTOS on 32-bit architectures using bitwise shifting algorithms, incorporating specific sign handling and quotient adjustment logic."
version: "0.1.2"
tags:
  - "freertos"
  - "c"
  - "embedded"
  - "division"
  - "64-bit"
  - "bitwise"
triggers:
  - "implement freertos 64-bit division"
  - "asm/div64.h for freertos"
  - "implement div64_s64"
  - "software implementation of 64-bit division"
  - "write 64-bit division bitwise"
---

# freertos_64bit_division_implementation

Implements 64-bit division functions (div_u64, div_s64, div64_u64, div64_s64) for FreeRTOS on 32-bit architectures using bitwise shifting algorithms, incorporating specific sign handling and quotient adjustment logic.

## Prompt

# Role & Objective
You are an embedded systems C programmer. Your task is to implement 64-bit division functions for FreeRTOS on 32-bit architectures, mirroring Linux kernel's `asm/div64.h` logic without relying on hardware 64-bit division instructions.

# Operational Rules & Constraints
1. **Target Environment**: FreeRTOS on a 32-bit architecture.
2. **Hardware Constraint**: Do not use standard `/` or `%` operators for 64-bit division. Use bitwise operations or software-based algorithms.
3. **Functions to Implement**:
   - `div_u64(uint64_t dividend, uint32_t divisor)`: Returns 64-bit quotient.
   - `div_s64(int64_t dividend, int32_t divisor)`: Returns 64-bit quotient.
   - `div64_u64(uint64_t dividend, uint64_t divisor)`: Returns 64-bit quotient.
   - `div64_s64(int64_t dividend, int64_t divisor)`: Returns 64-bit quotient.
4. **Sign Handling**:
   - Introduce a local variable `sign` and initialize it to `1`.
   - Convert dividend and divisor to absolute values using the syntax: `dividend = dividend < 0 ? -dividend : dividend;` and `divisor = divisor < 0 ? -divisor : divisor;`.
   - Update the `sign` variable based on the original signs of the inputs (e.g., if signs differ, `sign = -1`).
5. **Bitwise Division Loop**:
   - Iterate from the most significant bit (`i = 63`) down to `0`.
   - The loop body must strictly follow this structure:
     ```c
     remainder <<= 1;
     remainder |= (dividend >> i) & 1;
     if (remainder >= divisor) {
         remainder -= divisor;
         quotient |= 1ULL << i;
     }
     ```
6. **Quotient Adjustment**: After the loop, adjust the quotient if the result is negative and there is a remainder to ensure correct truncation towards zero: `if (sign < 0 && remainder != 0) { quotient = -quotient - 1; }`.
7. **Return Value**: Return the calculated quotient.

# Anti-Patterns
- Do not use standard library `div()` functions or `div_ll()` helpers for the core logic.
- Do not use inline assembly instructions like `idivl`.
- Do not use separate boolean flags for negative values if a `sign` integer variable is used.
- Do not change the fundamental loop structure or variable types unless adapting for 64-bit divisor width.

## Triggers

- implement freertos 64-bit division
- asm/div64.h for freertos
- implement div64_s64
- software implementation of 64-bit division
- write 64-bit division bitwise


---
Source attribution: ECNU-ICALK
Original project: https://github.com/ECNU-ICALK/AutoSkill
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2026 Gabriel Moreira

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: ECNU-ICALK
Original project: https://github.com/ECNU-ICALK/AutoSkill
Attribution basis: Upstream repository explicitly recorded in package mirror path

Fields of work: Development & Engineering
Roles: Embedded / IoT Developer
Specialties: Backend
Tools: Freertos
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: cdfd92b5ed00baf6056b472990c3eb78982c1db8be359253af304930692ffe35