[libc][math] Implement double precision expm1 function correctly rounded for all rounding modes. - #67048
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Overall LGTM from the libc side, with minor nits.
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Did you mean to leave the debug code in here?
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I found myself retyping these debug codes quite many times, and I couldn't find a better place to share this type of debugging codes yet. So I think I should leave it at least in one function so that a simple copy paste during development of other functions would be enough.
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should this one have a comment on its value as well?
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✅ With the latest revision this PR passed the C/C++ code formatter. |
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looks good to me. All core-math tests do pass for all 4 rounding modes, and efficiency is quite good: (first timings are for core-math, last for llvm) |
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…ded for all rounding modes. (llvm#67048) Implementing expm1 function for double precision based on exp function algorithm: - Reduced x = log2(e) * (hi + mid1 + mid2) + lo, where: * hi is an integer * mid1 * 2^-6 is an integer * mid2 * 2^-12 is an integer * |lo| < 2^-13 + 2^-30 - Then exp(x) - 1 = 2^hi * 2^mid1 * 2^mid2 * exp(lo) - 1 ~ 2^hi * (2^mid1 * 2^mid2 * (1 + lo * P(lo)) - 2^(-hi) ) - We evaluate fast pass with P(lo) is a degree-3 Taylor polynomial of (e^lo - 1) / lo in double precision - If the Ziv accuracy test fails, we use degree-6 Taylor polynomial of (e^lo - 1) / lo in double double precision - If the Ziv accuracy test still fails, we re-evaluate everything in 128-bit precision.
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Implementing expm1 function for double precision based on exp function algorithm: