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Remove unnecessary mask in exp() approximation

This isn't necessary since valid exponents can't flip the sign bit

--- a/dnn/vec_avx.h

+++ b/dnn/vec_avx.h

@@ -47,7 +47,6 @@

    const __m256 log2_E = _mm256_set1_ps(1.44269504);

    const __m256 max_in = _mm256_set1_ps(50.f);

    const __m256 min_in = _mm256_set1_ps(-50.f);

-   const __m256i mask = _mm256_set1_epi32(0x7fffffff);

    __m256 XF, Y;

    __m256i I;

    X = _mm256_mul_ps(X, log2_E);

@@ -57,7 +56,7 @@

    X = _mm256_sub_ps(X, XF);

    Y = _mm256_fmadd_ps(_mm256_fmadd_ps(_mm256_fmadd_ps(K3, X, K2), X, K1), X, K0);

    I = _mm256_slli_epi32(I, 23);

-   Y = _mm256_castsi256_ps(_mm256_and_si256(mask, _mm256_add_epi32(I, _mm256_castps_si256(Y))));

+   Y = _mm256_castsi256_ps(_mm256_add_epi32(I, _mm256_castps_si256(Y)));

    return Y;

 }

 #else

-- 

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