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Rev 80719 Rev 84215
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     *              =IEEE=  38.58601
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     *              =IEEE=  38.58601
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     * [on one x86_64 platform, effective boundary a bit lower: 38.56804]
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     * [on one x86_64 platform, effective boundary a bit lower: 38.56804]
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     */
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     */
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    if (x > sqrt(-2*M_LN2*(DBL_MIN_EXP + 1-DBL_MANT_DIG))) return 0.;
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    if (x > sqrt(-2*M_LN2*(DBL_MIN_EXP + 1-DBL_MANT_DIG))) return 0.;
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    /* Now, to get full accurary, split x into two parts,
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    /* Now, to get full accuracy, split x into two parts,
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     *  x = x1+x2, such that |x2| <= 2^-16.
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     *  x = x1+x2, such that |x2| <= 2^-16.
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     * Assuming that we are using IEEE doubles, that means that
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     * Assuming that we are using IEEE doubles, that means that
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     * x1*x1 is error free for x<1024 (but we have x < 38.6 anyway).
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     * x1*x1 is error free for x<1024 (but we have x < 38.6 anyway).
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     * If we do not have IEEE this is still an improvement over the naive formula.
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     * If we do not have IEEE this is still an improvement over the naive formula.