Enhance precision and safety in time calculations #483
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Introduce a new inline function mult_frac() to compute "x * n / d" with enhanced precision and safety. This function addresses the common issues of overflow and loss of precision that can occur with straightforward approaches to this calculation. Directly computing "x * n / d" can lead to problems: - Performing the division first can result in loss of precision due to integer truncation. - Performing multiplication before division can risk overflow. The mult_frac() function mitigates these issues by: 1. Calculating the quotient and remainder of 'x' divided by 'd'. 2. Using these intermediate results to perform the final calculation, thus avoiding intermediate overflow and preserving precision. This approach is based on the Linux kernel's mult_frac() macro [1], which follows a similar method to handle these calculations robustly. Link: https://elixir.bootlin.com/linux/v6.10.7/source/include/linux/math.h#L121 [1]
Refactor the get_time_info() function to use the newly added mult_frac() function for calculations involving time conversions. This change improves precision and mitigates the risk of overflow in the following areas: - Converte the computation of nanoseconds from mach_absolute_time() using the timebase information. - Update the calculation of nanoseconds from clock() in low-resolution timer mode. These updates make the time calculations in get_time_info() more robust and reliable by leveraging the precise arithmetic capabilities of mult_frac(). This change enhances the overall accuracy of time-related computations in the code.
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Thank @visitorckw for contributing! |
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Jan 24, 2025
Enhance precision and safety in time calculations
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Introduces a new inline function, mult_frac(), to handle fractional multiplication with improved precision and safety by computing x * n / d while avoiding common issues like overflow and precision loss. Additionally, the get_time_info() function has been refactored to use mult_frac() for time-related calculations, including nanosecond conversions from mach_absolute_time() and clock() in low-resolution timer mode. These updates collectively enhance the accuracy and reliability of time computations throughout the codebase.