Freertos 64bit Division Implementation

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

Audit 0.4.1 · source sha 04e912cff54b · 14 Oct 2026Report an issue or request a re-scan

• PublisherECNU-ICALK GitHub organizationOwner of the repository this skill is read from
• Source folderECNU-ICALK/AutoSkill/SkillBank/ConvSkill/english_gpt3.5_8_GLM4.7/freertos_64bit_division_implementationThe exact folder we audited
• LicenceNot declaredAs the repository states it
• Commit pinned for this verdict04e912cff54bA new audit runs when the source changes
• Repository statusNot archivedLast push 157 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its 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.

---
id: "a9d80b9a-ac18-4643-bb6d-e082da651f2f"
name: "freertos_64bit_division_implementation"
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

Excerpt, first 3,260 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

git clone https://github.com/ECNU-ICALK/AutoSkill
git -C AutoSkill checkout 04e912cff54b

Works in

1. 2026-10-14
   ✓SAFE B 89 / 100

   first audit · source 04e912cff54b

Questions about Freertos 64bit Division Implementation

• github.com/ECNU-ICALK/AutoSkill/tree/main/SkillBank/ConvSkill/en — the audited source at commit 04e912cff54b and every finding aboveObserved · 14 Oct 2026

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