[Beignet] [PATCH] utests: fix test case builtin_tgamma.

[Song, Ruiling]

> -----Original Message-----
> From: Beignet [mailto:beignet-bounces at lists.freedesktop.org] On Behalf Of
> Rebecca N. Palmer
> Sent: Thursday, April 23, 2015 10:33 PM
> To: beignet at lists.freedesktop.org
> Subject: Re: [Beignet] [PATCH] utests: fix test case builtin_tgamma.
> 
> > Should use tgamma instead of tgammaf when generating reference.
> That I agree with: we don't want the error of libc tgammaf (~4ulp) appearing
> to be our error.
> 
> > And the ulp bound is <= 16ulp
> That I wouldn't: it's defined in terms of the infinitely precise value, not the
> correctly-rounded-float value, so (e.g.)16.3ulp would round to 16ulp and
> pass the test when it shouldn't.
Yeah, this makes sense for me.

> Also, if it's that close to failing for positive inputs, it probably fails for
> negative inputs (which this test currently doesn't test).
> 
> > I find that even with your patch the builtin_tgamma still fails.
> For me the maximum error is 8ulp on the old test (i.e. positive input and
> including tgammaf's error), 4ulp (positive input) 6ulp (negative
> input) on my fixed test, so this is a real hardware-dependent error not just
> test issues.  What result do you get with this patch?

On the old test (using tgammaf):
What I got was "max error=186.000000 ulp at x=34.633003"
Src: 34.633003   cpu: 0x1.e56c58p+125 gpu: 0x1.e56dccp+125
While tgamma returns 0x1.e56dcap+125 for this input.
looks like tgammaf on my platform has big ulp error.

With your patch:
max error=6.000000 ulp at x=-29.857000
> 
> --------
> 
> Compare with tgamma instead of tgammaf for better accuracy.
> Include negative inputs, and handle the resulting denormals.
> Print maximum error found.
> 
> Signed-off-by: Rebecca Palmer <rebecca_palmer at zoho.com>
> 
> diff --git a/utests/builtin_tgamma.cpp b/utests/builtin_tgamma.cpp index
> 47cc5f4..b7db69b 100644
> --- a/utests/builtin_tgamma.cpp
> +++ b/utests/builtin_tgamma.cpp
> @@ -20,10 +20,15 @@ void builtin_tgamma(void)
>     if (env_strict == NULL || strcmp(env_strict, "0") == 0)
>       ULPSIZE_FACTOR = 10000.;
> 
> -  for (int j = 0; j < 1024; j ++) {
> +  cl_device_fp_config fp_config;
> +  clGetDeviceInfo(device, CL_DEVICE_SINGLE_FP_CONFIG,
> + sizeof(cl_device_fp_config), &fp_config, 0);  bool denormals_supported
> + = fp_config & CL_FP_DENORM;  float max_ulp = 0, max_ulp_at = 0;
> +
> +  for (int j = 0; j < 128; j ++) {
>       OCL_MAP_BUFFER(0);
>       for (int i = 0; i < n; ++i) {
> -      src[i] = ((float*)buf_data[0])[i] = (j*n+i+1) * 0.001f;
> +      src[i] = ((float*)buf_data[0])[i] = j - 64 + i*0.001f;
>       }
>       OCL_UNMAP_BUFFER(0);
> 
> @@ -32,7 +37,14 @@ void builtin_tgamma(void)
>       OCL_MAP_BUFFER(1);
>       float *dst = (float*)buf_data[1];
>       for (int i = 0; i < n; ++i) {
> -      float cpu = tgammaf(src[i]);
> +      float cpu = tgamma(src[i]);
> +      if (!denormals_supported && std::fpclassify(cpu)==FP_SUBNORMAL
> && dst[i]==0) {
> +        cpu = 0;
> +      }
> +      if (fabsf(cpu - dst[i]) > cl_FLT_ULP(cpu) * max_ulp) {
> +        max_ulp = fabsf(cpu - dst[i]) / cl_FLT_ULP(cpu);
> +        max_ulp_at = src[i];
> +      }
>         if (isinf(cpu)) {
>           OCL_ASSERT(isinf(dst[i]));
>         } else if (fabsf(cpu - dst[i]) >= cl_FLT_ULP(cpu) * ULPSIZE_FACTOR)
> { @@ -42,6 +54,7 @@ void builtin_tgamma(void)
>       }
>       OCL_UNMAP_BUFFER(1);
>     }
> +  printf("max error=%f ulp at x=%f ", max_ulp, max_ulp_at);
>   }
> 
>   MAKE_UTEST_FROM_FUNCTION(builtin_tgamma);
> 
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