[Beignet] [PATCH] backend: refine math log function

[Yang, Rong R]

LGTM, pushed, thanks.

> -----Original Message-----
> From: Beignet [mailto:beignet-bounces at lists.freedesktop.org] On Behalf Of
> rander.wang
> Sent: Monday, June 19, 2017 13:21
> To: beignet at freedesktop.org
> Cc: Wang, Rander <rander.wang at intel.com>
> Subject: [Beignet] [PATCH] backend: refine math log function
> 
> 	remove a few unnecessary codes , and get 20% improvement
> 	at worse case. If X is a NAN, there are some if-return
> 	codes to return NAN. Now change it to add(x - x) which
> 	get the same NAN
> 
> 	pass the conformance tests and utests
> 
> Signed-off-by: rander.wang <rander.wang at intel.com>
> ---
>  backend/src/libocl/tmpl/ocl_math_common.tmpl.cl | 50 +++++----------------
> ----
>  1 file changed, 10 insertions(+), 40 deletions(-)
> 
> diff --git a/backend/src/libocl/tmpl/ocl_math_common.tmpl.cl
> b/backend/src/libocl/tmpl/ocl_math_common.tmpl.cl
> index b4764ee..2c0a702 100644
> --- a/backend/src/libocl/tmpl/ocl_math_common.tmpl.cl
> +++ b/backend/src/libocl/tmpl/ocl_math_common.tmpl.cl
> @@ -201,38 +201,19 @@ OVERLOADABLE float inline
> __gen_ocl_internal_log_valid(float x) {
>    k += (i>>23);
>    f = x - 1.0f;
>    fsq = f * f;
> -
> -  if((0x007fffff & (15 + ix)) < 16) { /* |f| < 2**-20 */
> -      R = fsq * (0.5f - 0.33333333333333333f * f);
> -      return k * ln2_hi + k * ln2_lo + f - R;
> -  }
> -
> -  s = f / (2.0f + f);
> +  s = mad(-2.0f, 1.0f / (2.0f + f), 1.0f);
>    z = s * s;
> -  i = ix - (0x6147a << 3);
>    w = z * z;
> -  j = (0x6b851 << 3) - ix;
> -  t1= w * mad(w, Lg4, Lg2);
> -  t2= z * mad(w, Lg3, Lg1);
> -  i |= j;
> -  R = t2 + t1;
> -  partial = (i > 0) ? -mad(s, 0.5f * fsq, -0.5f * fsq) : (s * f);
> -
> -  return mad(s, R, f) - partial + k * ln2_hi + k * ln2_lo;;
> +  t1 = w * mad(w, Lg4, Lg2);
> +  R = mad(z, mad(w, Lg3, Lg1), t1);
> +  w = 0.5f * fsq;
> +  partial = -mad(s, w, -w);
> +  return mad(k, ln2_lo, mad(k, ln2_hi, mad(s, R, f) - partial));
>  }
> 
>  OVERLOADABLE float __gen_ocl_internal_log(float x)  {
> -  union { unsigned int i; float f; } u;
> -  u.f = x;
> -  int ix = u.i;
> -
> -  if (ix < 0 )
> -	return NAN;  /* log(-#) = NaN */
> -  if (ix >= 0x7f800000)
> -    return NAN;
> -
> -  return __gen_ocl_internal_log_valid(x);
> +  return __gen_ocl_internal_log_valid(x) + (x - x);
>  }
> 
>  OVERLOADABLE float __gen_ocl_internal_log10(float x) @@ -244,12 +225,10
> @@ OVERLOADABLE float __gen_ocl_internal_log10(float x)
>    log10_2lo  =  7.9034151668e-07; /* 0x355427db */
> 
>    float y, z;
> -  int i, k, hx;
> +  int i, k;
> +  unsigned int hx;
> 
>    u.f = x; hx = u.i;
> -
> -  if (hx<0)
> -    return NAN; /* log(-#) = NaN */
>    if (hx >= 0x7f800000)
>      return NAN;
> 
> @@ -267,17 +246,8 @@ OVERLOADABLE float __gen_ocl_internal_log2(float
> x)  {
>    const float zero   =  0.0,
>    invln2 = 0x1.715476p+0f;
> -  int ix;
> -
> -  union { float f; int i; } u;
> -  u.f = x; ix = u.i;
> -
> -  if (ix < 0)
> -	return NAN;    /** log(-#) = NaN */
> -  if (ix >= 0x7f800000)
> -	return NAN;
> 
> -  return invln2 * __gen_ocl_internal_log_valid(x);
> +  return invln2 * __gen_ocl_internal_log_valid(x) + (x - x);
>  }
> 
> 
> --
> 2.7.4
> 
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