[Beignet] [PATCH] backend: refine exp function with float input

[Yang, Rong R]

Pushed, thanks.

> -----Original Message-----
> From: Beignet [mailto:beignet-bounces at lists.freedesktop.org] On Behalf Of
> Pan, Xiuli
> Sent: Wednesday, June 7, 2017 15:52
> To: Wang, Rander <rander.wang at intel.com>; beignet at freedesktop.org
> Cc: Wang, Rander <rander.wang at intel.com>
> Subject: Re: [Beignet] [PATCH] backend: refine exp function with float input
> 
> LGTM.
> Thanks
> 
> 
> -----Original Message-----
> From: Beignet [mailto:beignet-bounces at lists.freedesktop.org] On Behalf Of
> rander.wang
> Sent: Wednesday, June 7, 2017 15:47
> To: beignet at freedesktop.org
> Cc: Wang, Rander <rander.wang at intel.com>
> Subject: [Beignet] [PATCH] backend: refine exp function with float input
> 
> 	remove some corner cases check for these path can not be
> 	reached.And refine branch code to select. These improvements
> 	get 20% performance. and the performance of  OCL_ExpFixture_Exp
>         in opencv can match up to other Gen driver
> 
> Signed-off-by: rander.wang <rander.wang at intel.com>
> ---
>  backend/src/libocl/tmpl/ocl_math_common.tmpl.cl | 60
> ++++++++++++++++++++++++-
>  1 file changed, 58 insertions(+), 2 deletions(-)
> 
> diff --git a/backend/src/libocl/tmpl/ocl_math_common.tmpl.cl
> b/backend/src/libocl/tmpl/ocl_math_common.tmpl.cl
> index 6b942db..6286ea6 100644
> --- a/backend/src/libocl/tmpl/ocl_math_common.tmpl.cl
> +++ b/backend/src/libocl/tmpl/ocl_math_common.tmpl.cl
> @@ -1418,6 +1418,62 @@ OVERLOADABLE float
> __gen_ocl_internal_exp(float x) {
>    }
>  }
> 
> +OVERLOADABLE float __gen_ocl_internal_simple_exp(float x) {
> +  float o_threshold = 8.8721679688e+01,  /* 0x42b17180 */
> +  u_threshold = -1.0397208405e+02,  /* 0xc2cff1b5 */
> +  twom100 = 7.8886090522e-31, /* 2**-100=0x0d800000 */
> +  ivln2 = 1.4426950216e+00, /* 0x3fb8aa3b =1/ln2 */
> +  one = 1.0,
> +  P1 = 1.6666667163e-01, /* 0x3e2aaaab */
> +  P2 = -2.7777778450e-03; /* 0xbb360b61 */
> +  float y,hi=0.0,lo=0.0,c,t;
> +  int k=0;
> +  unsigned hx;
> +  float ln2HI_0 = 6.9313812256e-01; /* 0x3f317180 */
> +  float ln2HI_1 = -6.9313812256e-01; /* 0xbf317180 */
> +  float ln2LO_0 = 9.0580006145e-06;  	/* 0x3717f7d1 */
> +  float ln2LO_1 = -9.0580006145e-06; /* 0xb717f7d1 */
> +  float half_0 = 0.5;
> +  float half_1 = -0.5;
> +  float retVal = -1.0f;
> +  hx = as_uint(fabs(x));
> +
> +  /* filter out non-finite argument */
> +  /* if |x|>=88.721... */
> +  if(hx >= 0x42b17218)
> +  {
> +    float tmp = (x > 0)? x:0.0;
> +    retVal = (x > 0)? INFINITY:retVal; /* overflow */
> +    retVal = (hx>0x7f800000)? NAN:retVal;
> +    retVal = (hx==0x7f800000)? tmp:retVal;
> +    retVal = (x < u_threshold)? 0.0:retVal; /* underflow */
> +
> +    if(retVal != -1.0f)
> +      return retVal;
> +  }
> +
> +  /* argument reduction */
> +  float tmp = (x < 0) ? half_1 : half_0;  k  = mad(ivln2, x, tmp);  t =
> + k;  hi = mad(t, -ln2HI_0, x); /* t*ln2HI is exact here */  lo =
> + t*ln2LO_0;  x  = hi - lo;
> +
> +  /* x is now in primary range */
> +  t  = x*x;
> +  c  = mad(t, mad(t, -P2, -P1), x);
> +  y = one-((lo + (x*c)/(c-2.0f))-hi);
> +
> +  unsigned hy;
> +  GEN_OCL_GET_FLOAT_WORD(hy,y);
> +
> +  float factor = (k >= -125)? 1.0f:twom100;
> +  k = (k >= -125)? k:k+100;
> +  GEN_OCL_SET_FLOAT_WORD(y,hy+(k<<23)); /* add k to y's exponent */
> +  return y*factor;
> +}
> +
>  /* erf,erfc from glibc s_erff.c -- float version of s_erf.c.
>   * Conversion to float by Ian Lance Taylor, Cygnus Support, ian at cygnus.com.
>   */
> @@ -3105,10 +3161,10 @@ OVERLOADABLE float exp(float x) {
>      return __gen_ocl_internal_fastpath_exp(x);
> 
>    /* Use native instruction when it has enough precision */
> -  if (x > -0x1.6p1 && x < 0x1.6p1)
> +  if (fabs(x) < 0x1.6p1)
>      return __gen_ocl_internal_fastpath_exp(x);
> 
> -  return  __gen_ocl_internal_exp(x);
> +  return  __gen_ocl_internal_simple_exp(x);
>  }
> 
>  OVERLOADABLE float exp2(float x) {
> --
> 2.7.4
> 
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