OpenCL 的精度，hello world 示例中的浮点比较
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【中文标题】OpenCL 的精度，hello world 示例中的浮点比较【英文标题】：Precision with OpenCL, float comparison in the hello world sample 【发布时间】：2012-06-17 12:12:30 【问题描述】：我要学习 OpenCL，想轻松上手。
我发现并修改了这个 hello world 示例，但没有任何必要。 http://developer.apple.com/library/mac/#samplecode/OpenCL_Hello_World_Example/Introduction/Intro.html
//
// File: hello.c
//
// Abstract: A simple "Hello World" compute example showing basic usage of OpenCL which
// calculates the mathematical square (X[i] = pow(X[i],2)) for a buffer of
// floating point values.
//
//
// Version: <1.0>
//
// Disclaimer: IMPORTANT: This Apple software is supplied to you by Apple Inc. ("Apple")
// in consideration of your agreement to the following terms, and your use,
// installation, modification or redistribution of this Apple software
// constitutes acceptance of these terms. If you do not agree with these
// terms, please do not use, install, modify or redistribute this Apple
// software.
//
// In consideration of your agreement to abide by the following terms, and
// subject to these terms, Apple grants you a personal, non - exclusive
// license, under Apple's copyrights in this original Apple software ( the
// "Apple Software" ), to use, reproduce, modify and redistribute the Apple
// Software, with or without modifications, in source and / or binary forms;
// provided that if you redistribute the Apple Software in its entirety and
// without modifications, you must retain this notice and the following text
// and disclaimers in all such redistributions of the Apple Software. Neither
// the name, trademarks, service marks or logos of Apple Inc. may be used to
// endorse or promote products derived from the Apple Software without specific
// prior written permission from Apple. Except as expressly stated in this
// notice, no other rights or licenses, express or implied, are granted by
// Apple herein, including but not limited to any patent rights that may be
// infringed by your derivative works or by other works in which the Apple
// Software may be incorporated.
//
// The Apple Software is provided by Apple on an "AS IS" basis. APPLE MAKES NO
// WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION THE IMPLIED
// WARRANTIES OF NON - INFRINGEMENT, MERCHANTABILITY AND FITNESS FOR A
// PARTICULAR PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND OPERATION
// ALONE OR IN COMBINATION WITH YOUR PRODUCTS.
//
// IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL OR
// CONSEQUENTIAL DAMAGES ( INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION ) ARISING IN ANY WAY OUT OF THE USE, REPRODUCTION, MODIFICATION
// AND / OR DISTRIBUTION OF THE APPLE SOFTWARE, HOWEVER CAUSED AND WHETHER
// UNDER THEORY OF CONTRACT, TORT ( INCLUDING NEGLIGENCE ), STRICT LIABILITY OR
// OTHERWISE, EVEN IF APPLE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Copyright ( C ) 2008 Apple Inc. All Rights Reserved.
//
////////////////////////////////////////////////////////////////////////////////
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
//#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <CL/opencl.h>
#define Warning(...) fprintf(stderr, __VA_ARGS__)
////////////////////////////////////////////////////////////////////////////////
// Use a static data size for simplicity
//
#define DATA_SIZE (1024)
////////////////////////////////////////////////////////////////////////////////
// Simple compute kernel which computes the square of an input array
//
const char *KernelSource = "\n" \
"__kernel void square( \n" \
" __global float* input, \n" \
" __global float* output, \n" \
" const unsigned int count) \n" \
" \n" \
" int i = get_global_id(0); \n" \
" if(i < count) \n" \
" output[i] = input[i] * input[i]; \n" \
" \n" \
"\n";
////////////////////////////////////////////////////////////////////////////////
/*
* CLErrString --
*
* Utility function that converts an OpenCL status into a human
* readable string.
*
* Results:
* const char * pointer to a static string.
*/
static const char *
CLErrString(cl_int status)
static struct cl_int code; const char *msg; error_table[] =
CL_SUCCESS, "success" ,
CL_DEVICE_NOT_FOUND, "device not found", ,
CL_DEVICE_NOT_AVAILABLE, "device not available", ,
CL_COMPILER_NOT_AVAILABLE, "compiler not available", ,
CL_MEM_OBJECT_ALLOCATION_FAILURE, "mem object allocation failure", ,
CL_OUT_OF_RESOURCES, "out of resources", ,
CL_OUT_OF_HOST_MEMORY, "out of host memory", ,
CL_PROFILING_INFO_NOT_AVAILABLE, "profiling not available", ,
CL_MEM_COPY_OVERLAP, "memcopy overlaps", ,
CL_IMAGE_FORMAT_MISMATCH, "image format mismatch", ,
CL_IMAGE_FORMAT_NOT_SUPPORTED, "image format not supported", ,
CL_BUILD_PROGRAM_FAILURE, "build program failed", ,
CL_MAP_FAILURE, "map failed", ,
CL_INVALID_VALUE, "invalid value", ,
CL_INVALID_DEVICE_TYPE, "invalid device type", ,
0, NULL ,
;
static char unknown[25];
int ii;
for (ii = 0; error_table[ii].msg != NULL; ii++)
if (error_table[ii].code == status)
return error_table[ii].msg;
_snprintf(unknown, sizeof unknown, "unknown error %d", status);
return unknown;
/*
* PrintDevice --
*
* Dumps everything about the given device ID.
*
* Results:
* void.
*/
static void
PrintDevice(cl_device_id device)
#define LONG_PROPS \
defn(VENDOR_ID), \
defn(MAX_COMPUTE_UNITS), \
defn(MAX_WORK_ITEM_DIMENSIONS), \
defn(MAX_WORK_GROUP_SIZE), \
defn(PREFERRED_VECTOR_WIDTH_CHAR), \
defn(PREFERRED_VECTOR_WIDTH_SHORT), \
defn(PREFERRED_VECTOR_WIDTH_INT), \
defn(PREFERRED_VECTOR_WIDTH_LONG), \
defn(PREFERRED_VECTOR_WIDTH_FLOAT), \
defn(PREFERRED_VECTOR_WIDTH_DOUBLE), \
defn(MAX_CLOCK_FREQUENCY), \
defn(ADDRESS_BITS), \
defn(MAX_MEM_ALLOC_SIZE), \
defn(IMAGE_SUPPORT), \
defn(MAX_READ_IMAGE_ARGS), \
defn(MAX_WRITE_IMAGE_ARGS), \
defn(IMAGE2D_MAX_WIDTH), \
defn(IMAGE2D_MAX_HEIGHT), \
defn(IMAGE3D_MAX_WIDTH), \
defn(IMAGE3D_MAX_HEIGHT), \
defn(IMAGE3D_MAX_DEPTH), \
defn(MAX_SAMPLERS), \
defn(MAX_PARAMETER_SIZE), \
defn(MEM_BASE_ADDR_ALIGN), \
defn(MIN_DATA_TYPE_ALIGN_SIZE), \
defn(GLOBAL_MEM_CACHELINE_SIZE), \
defn(GLOBAL_MEM_CACHE_SIZE), \
defn(GLOBAL_MEM_SIZE), \
defn(MAX_CONSTANT_BUFFER_SIZE), \
defn(MAX_CONSTANT_ARGS), \
defn(LOCAL_MEM_SIZE), \
defn(ERROR_CORRECTION_SUPPORT), \
defn(PROFILING_TIMER_RESOLUTION), \
defn(ENDIAN_LITTLE), \
defn(AVAILABLE), \
defn(COMPILER_AVAILABLE),
#define STR_PROPS \
defn(NAME), \
defn(VENDOR), \
defn(PROFILE), \
defn(VERSION), \
defn(EXTENSIONS),
#define HEX_PROPS \
defn(SINGLE_FP_CONFIG), \
defn(QUEUE_PROPERTIES),
/* XXX For completeness, it'd be nice to dump this one, too. */
#define WEIRD_PROPS \
CL_DEVICE_MAX_WORK_ITEM_SIZES,
static struct cl_device_info param; const char *name; longProps[] =
#define defn(X) CL_DEVICE_##X, #X
LONG_PROPS
#undef defn
0, NULL ,
;
static struct cl_device_info param; const char *name; hexProps[] =
#define defn(X) CL_DEVICE_##X, #X
HEX_PROPS
#undef defn
0, NULL ,
;
static struct cl_device_info param; const char *name; strProps[] =
#define defn(X) CL_DEVICE_##X, #X
STR_PROPS
#undef defn
CL_DRIVER_VERSION, "DRIVER_VERSION" ,
0, NULL ,
;
cl_int status;
size_t size;
char buf[65536];
long long val; /* Avoids unpleasant surprises for some params */
int ii;
for (ii = 0; strProps[ii].name != NULL; ii++)
status = clGetDeviceInfo(device, strProps[ii].param, sizeof buf, buf, &size);
if (status != CL_SUCCESS)
Warning("\tdevice[%p]: Unable to get %s: %s!\n",
device, strProps[ii].name, CLErrString(status));
continue;
if (size > sizeof buf)
Warning("\tdevice[%p]: Large %s (%d bytes)! Truncating to %d!\n",
device, strProps[ii].name, size, sizeof buf);
printf("\tdevice[%p]: %s: %s\n",
device, strProps[ii].name, buf);
printf("\n");
status = clGetDeviceInfo(device, CL_DEVICE_TYPE, sizeof val, &val, NULL);
if (status == CL_SUCCESS)
printf("\tdevice[%p]: Type: ", device);
if (val & CL_DEVICE_TYPE_DEFAULT)
val &= ~CL_DEVICE_TYPE_DEFAULT;
printf("Default ");
if (val & CL_DEVICE_TYPE_CPU)
val &= ~CL_DEVICE_TYPE_CPU;
printf("CPU ");
if (val & CL_DEVICE_TYPE_GPU)
val &= ~CL_DEVICE_TYPE_GPU;
printf("GPU ");
if (val & CL_DEVICE_TYPE_ACCELERATOR)
val &= ~CL_DEVICE_TYPE_ACCELERATOR;
printf("Accelerator ");
if (val != 0)
printf("Unknown (0x%llx) ", val);
printf("\n");
else
Warning("\tdevice[%p]: Unable to get TYPE: %s!\n",
device, CLErrString(status));
status = clGetDeviceInfo(device, CL_DEVICE_EXECUTION_CAPABILITIES,
sizeof val, &val, NULL);
if (status == CL_SUCCESS)
printf("\tdevice[%p]: EXECUTION_CAPABILITIES: ", device);
if (val & CL_EXEC_KERNEL)
val &= ~CL_EXEC_KERNEL;
printf("Kernel ");
if (val & CL_EXEC_NATIVE_KERNEL)
val &= ~CL_EXEC_NATIVE_KERNEL;
printf("Native ");
if (val)
printf("Unknown (0x%llx) ", val);
printf("\n");
else
Warning("\tdevice[%p]: Unable to get EXECUTION_CAPABILITIES: %s!\n",
device, CLErrString(status));
status = clGetDeviceInfo(device, CL_DEVICE_GLOBAL_MEM_CACHE_TYPE,
sizeof val, &val, NULL);
if (status == CL_SUCCESS)
static const char *cacheTypes[] = "None", "Read-Only", "Read-Write" ;
static int numTypes = sizeof cacheTypes / sizeof cacheTypes[0];
printf("\tdevice[%p]: GLOBAL_MEM_CACHE_TYPE: %s (%lld)\n",
device, val < numTypes ? cacheTypes[val] : "???", val);
else
Warning("\tdevice[%p]: Unable to get GLOBAL_MEM_CACHE_TYPE: %s!\n",
device, CLErrString(status));
status = clGetDeviceInfo(device,
CL_DEVICE_LOCAL_MEM_TYPE, sizeof val, &val, NULL);
if (status == CL_SUCCESS)
static const char *lmemTypes[] = "???", "Local", "Global" ;
static int numTypes = sizeof lmemTypes / sizeof lmemTypes[0];
printf("\tdevice[%p]: CL_DEVICE_LOCAL_MEM_TYPE: %s (%lld)\n",
device, val < numTypes ? lmemTypes[val] : "???", val);
else
Warning("\tdevice[%p]: Unable to get CL_DEVICE_LOCAL_MEM_TYPE: %s!\n",
device, CLErrString(status));
for (ii = 0; hexProps[ii].name != NULL; ii++)
status = clGetDeviceInfo(device, hexProps[ii].param, sizeof val, &val, &size);
if (status != CL_SUCCESS)
Warning("\tdevice[%p]: Unable to get %s: %s!\n",
device, hexProps[ii].name, CLErrString(status));
continue;
if (size > sizeof val)
Warning("\tdevice[%p]: Large %s (%d bytes)! Truncating to %d!\n",
device, hexProps[ii].name, size, sizeof val);
printf("\tdevice[%p]: %s: 0x%llx\n",
device, hexProps[ii].name, val);
printf("\n");
for (ii = 0; longProps[ii].name != NULL; ii++)
status = clGetDeviceInfo(device, longProps[ii].param, sizeof val, &val, &size);
if (status != CL_SUCCESS)
Warning("\tdevice[%p]: Unable to get %s: %s!\n",
device, longProps[ii].name, CLErrString(status));
continue;
if (size > sizeof val)
Warning("\tdevice[%p]: Large %s (%d bytes)! Truncating to %d!\n",
device, longProps[ii].name, size, sizeof val);
printf("\tdevice[%p]: %s: %lld\n",
device, longProps[ii].name, val);
/*
* PrintPlatform --
*
* Dumps everything about the given platform ID.
*
* Results:
* void.
*/
static void
PrintPlatform(cl_platform_id platform)
static struct cl_platform_info param; const char *name; props[] =
CL_PLATFORM_PROFILE, "profile" ,
CL_PLATFORM_VERSION, "version" ,
CL_PLATFORM_NAME, "name" ,
CL_PLATFORM_VENDOR, "vendor" ,
CL_PLATFORM_EXTENSIONS, "extensions" ,
0, NULL ,
;
cl_device_id *deviceList;
cl_uint numDevices;
cl_int status;
char buf[65536];
size_t size;
int ii;
for (ii = 0; props[ii].name != NULL; ii++)
status = clGetPlatformInfo(platform, props[ii].param, sizeof buf, buf, &size);
if (status != CL_SUCCESS)
Warning("platform[%p]: Unable to get %s: %s\n",
platform, props[ii].name, CLErrString(status));
continue;
if (size > sizeof buf)
Warning("platform[%p]: Huge %s (%d bytes)! Truncating to %d\n",
platform, props[ii].name, size, sizeof buf);
printf("platform[%p]: %s: %s\n", platform, props[ii].name, buf);
if ((status = clGetDeviceIDs(platform, CL_DEVICE_TYPE_ALL,
0, NULL, &numDevices)) != CL_SUCCESS)
Warning("platform[%p]: Unable to query the number of devices: %s\n",
platform, CLErrString(status));
return;
printf("platform[%p]: Found %d device(s).\n", platform, numDevices);
deviceList = (cl_device_id *)malloc(numDevices * sizeof(cl_device_id));
if ((status = clGetDeviceIDs(platform, CL_DEVICE_TYPE_ALL,
numDevices, deviceList, NULL)) != CL_SUCCESS)
Warning("platform[%p]: Unable to enumerate the devices: %s\n",
platform, CLErrString(status));
free(deviceList);
return;
for (ii = 0; ii < numDevices; ii++)
PrintDevice(deviceList[ii]);
free(deviceList);
int main(int argc, char** argv)
int err; // error code returned from api calls
float data[DATA_SIZE]; // original data set given to device
float results[DATA_SIZE]; // results returned from device
unsigned int correct; // number of correct results returned
size_t global; // global domain size for our calculation
size_t local; // local domain size for our calculation
cl_platform_id platform; // compute platform id
cl_uint numPlatforms;
cl_platform_id *platformList;
cl_int status;
cl_device_id device_id; // compute device id
cl_context context; // compute context
cl_command_queue commands; // compute command queue
cl_program program; // compute program
cl_kernel kernel; // compute kernel
cl_mem input; // device memory used for the input array
cl_mem output; // device memory used for the output array
// Fill our data set with random float values
//
int i = 0;
unsigned int count = DATA_SIZE;
for(i = 0; i < count; i++)
data[i] = rand() / (float)RAND_MAX;
// printf("%f\n",data[i]);
err = clGetPlatformIDs(1, &platform, &numPlatforms);
if(err < 0)
perror("Couldn't find any platforms");
return EXIT_FAILURE;
printf("Found %d platform(s).\n", numPlatforms);
platformList = (cl_platform_id *) malloc(sizeof(cl_platform_id) * numPlatforms);
if ((status = clGetPlatformIDs(numPlatforms, platformList, NULL)) != CL_SUCCESS)
Warning("Unable to enumerate the platforms: %s\n",
CLErrString(status));
exit(1);
int ii;
for (ii = 0; ii < numPlatforms; ii++)
PrintPlatform(platformList[ii]);
// Connect to a compute device
//
int gpu = 1;
err = clGetDeviceIDs(platformList[0], gpu ? CL_DEVICE_TYPE_GPU : CL_DEVICE_TYPE_CPU, 1, &device_id, NULL);
if (err != CL_SUCCESS)
printf("Error: Failed to create a device group!\n");
return EXIT_FAILURE;
// Create a compute context
//
context = clCreateContext(0, 1, &device_id, NULL, NULL, &err);
if (!context)
printf("Error: Failed to create a compute context!\n");
return EXIT_FAILURE;
// Create a command commands
//
commands = clCreateCommandQueue(context, device_id, 0, &err);
if (!commands)
printf("Error: Failed to create a command commands!\n");
return EXIT_FAILURE;
// Create the compute program from the source buffer
//
program = clCreateProgramWithSource(context, 1, (const char **) & KernelSource, NULL, &err);
if (!program)
printf("Error: Failed to create compute program!\n");
return EXIT_FAILURE;
// Build the program executable
//
err = clBuildProgram(program, 0, NULL, NULL, NULL, NULL);
if (err != CL_SUCCESS)
size_t len;
char buffer[2048];
printf("Error: Failed to build program executable!\n");
clGetProgramBuildInfo(program, device_id, CL_PROGRAM_BUILD_LOG, sizeof(buffer), buffer, &len);
printf("%s\n", buffer);
exit(1);
// Create the compute kernel in the program we wish to run
//
kernel = clCreateKernel(program, "square", &err);
if (!kernel || err != CL_SUCCESS)
printf("Error: Failed to create compute kernel!\n");
exit(1);
// Create the input and output arrays in device memory for our calculation
//
input = clCreateBuffer(context, CL_MEM_READ_ONLY, sizeof(float) * count, NULL, NULL);
output = clCreateBuffer(context, CL_MEM_WRITE_ONLY, sizeof(float) * count, NULL, NULL);
if (!input || !output)
printf("Error: Failed to allocate device memory!\n");
exit(1);
// Write our data set into the input array in device memory
//
err = clEnqueueWriteBuffer(commands, input, CL_TRUE, 0, sizeof(float) * count, data, 0, NULL, NULL);
if (err != CL_SUCCESS)
printf("Error: Failed to write to source array!\n");
exit(1);
// Set the arguments to our compute kernel
//
err = 0;
err = clSetKernelArg(kernel, 0, sizeof(cl_mem), &input);
err |= clSetKernelArg(kernel, 1, sizeof(cl_mem), &output);
err |= clSetKernelArg(kernel, 2, sizeof(unsigned int), &count);
if (err != CL_SUCCESS)
printf("Error: Failed to set kernel arguments! %d\n", err);
exit(1);
// Get the maximum work group size for executing the kernel on the device
//
err = clGetKernelWorkGroupInfo(kernel, device_id, CL_KERNEL_WORK_GROUP_SIZE, sizeof(local), &local, NULL);
if (err != CL_SUCCESS)
printf("Error: Failed to retrieve kernel work group info! %d\n", err);
exit(1);
// Execute the kernel over the entire range of our 1d input data set
// using the maximum number of work group items for this device
//
global = count;
err = clEnqueueNDRangeKernel(commands, kernel, 1, NULL, &global, &local, 0, NULL, NULL);
if (err)
printf("Error: Failed to execute kernel!\n");
return EXIT_FAILURE;
// Wait for the command commands to get serviced before reading back results
//
clFinish(commands);
// Read back the results from the device to verify the output
//
err = clEnqueueReadBuffer( commands, output, CL_TRUE, 0, sizeof(float) * count, results, 0, NULL, NULL );
if (err != CL_SUCCESS)
printf("Error: Failed to read output array! %d\n", err);
exit(1);
// Validate our results
//
correct = 0;
for(i = 0; i < count; i++)
//printf("%4f %4.10f %4.10f \n", data[i],data[i] * data[i], results[i]);
if((results[i] - data[i] * data[i]) < 10e-8)
correct++;
// Print a brief summary detailing the results
//
printf("Computed '%d/%d' correct values!\n", correct, count);
// Shutdown and cleanup
//
free(platformList);
clReleaseMemObject(input);
clReleaseMemObject(output);
clReleaseProgram(program);
clReleaseKernel(kernel);
clReleaseCommandQueue(commands);
clReleaseContext(context);
return 0;
我在 Geforce 8800 GTS 上运行。
F:\Documents\Dropbox\05030 - OpenCL\Samples\Debug>HelloWorld.exe
Found 1 platform(s).
platform[012C6F88]: profile: FULL_PROFILE
platform[012C6F88]: version: OpenCL 1.1 CUDA 4.2.1
platform[012C6F88]: name: NVIDIA CUDA
platform[012C6F88]: vendor: NVIDIA Corporation
platform[012C6F88]: extensions: cl_khr_byte_addressable_store cl_khr_icd cl_khr_
gl_sharing cl_nv_d3d9_sharing cl_nv_d3d10_sharing cl_khr_d3d10_sharing cl_nv_d3d
11_sharing cl_nv_compiler_options cl_nv_device_attribute_query cl_nv_pragma_unro
ll
platform[012C6F88]: Found 1 device(s).
device[012C6FF0]: NAME: GeForce 8800 GTS
device[012C6FF0]: VENDOR: NVIDIA Corporation
device[012C6FF0]: PROFILE: FULL_PROFILE
device[012C6FF0]: VERSION: OpenCL 1.0 CUDA
device[012C6FF0]: EXTENSIONS: cl_khr_byte_addressable_store cl_khr_icd c
l_khr_gl_sharing cl_nv_d3d9_sharing cl_nv_d3d10_sharing cl_khr_d3d10_sharing cl_
nv_d3d11_sharing cl_nv_compiler_options cl_nv_device_attribute_query cl_nv_pragm
a_unroll
device[012C6FF0]: DRIVER_VERSION: 301.42
device[012C6FF0]: Type: GPU
device[012C6FF0]: EXECUTION_CAPABILITIES: Kernel
device[012C6FF0]: GLOBAL_MEM_CACHE_TYPE: None (0)
device[012C6FF0]: CL_DEVICE_LOCAL_MEM_TYPE: Local (1)
device[012C6FF0]: SINGLE_FP_CONFIG: 0x3e
device[012C6FF0]: QUEUE_PROPERTIES: 0x3
device[012C6FF0]: VENDOR_ID: 4318
device[012C6FF0]: MAX_COMPUTE_UNITS: 12
device[012C6FF0]: MAX_WORK_ITEM_DIMENSIONS: 3
device[012C6FF0]: MAX_WORK_GROUP_SIZE: 512
device[012C6FF0]: PREFERRED_VECTOR_WIDTH_CHAR: 1
device[012C6FF0]: PREFERRED_VECTOR_WIDTH_SHORT: 1
device[012C6FF0]: PREFERRED_VECTOR_WIDTH_INT: 1
device[012C6FF0]: PREFERRED_VECTOR_WIDTH_LONG: 1
device[012C6FF0]: PREFERRED_VECTOR_WIDTH_FLOAT: 1
device[012C6FF0]: PREFERRED_VECTOR_WIDTH_DOUBLE: 0
device[012C6FF0]: MAX_CLOCK_FREQUENCY: 1188
device[012C6FF0]: ADDRESS_BITS: 32
device[012C6FF0]: MAX_MEM_ALLOC_SIZE: 134217728
device[012C6FF0]: IMAGE_SUPPORT: 1
device[012C6FF0]: MAX_READ_IMAGE_ARGS: 128
device[012C6FF0]: MAX_WRITE_IMAGE_ARGS: 8
device[012C6FF0]: IMAGE2D_MAX_WIDTH: 4096
device[012C6FF0]: IMAGE2D_MAX_HEIGHT: 16383
device[012C6FF0]: IMAGE3D_MAX_WIDTH: 2048
device[012C6FF0]: IMAGE3D_MAX_HEIGHT: 2048
device[012C6FF0]: IMAGE3D_MAX_DEPTH: 2048
device[012C6FF0]: MAX_SAMPLERS: 16
device[012C6FF0]: MAX_PARAMETER_SIZE: 4352
device[012C6FF0]: MEM_BASE_ADDR_ALIGN: 2048
device[012C6FF0]: MIN_DATA_TYPE_ALIGN_SIZE: 128
device[012C6FF0]: GLOBAL_MEM_CACHELINE_SIZE: 0
device[012C6FF0]: GLOBAL_MEM_CACHE_SIZE: 0
device[012C6FF0]: GLOBAL_MEM_SIZE: 335544320
device[012C6FF0]: MAX_CONSTANT_BUFFER_SIZE: 65536
device[012C6FF0]: MAX_CONSTANT_ARGS: 9
device[012C6FF0]: LOCAL_MEM_SIZE: 16384
device[012C6FF0]: ERROR_CORRECTION_SUPPORT: 0
device[012C6FF0]: PROFILING_TIMER_RESOLUTION: 1000
device[012C6FF0]: ENDIAN_LITTLE: 1
device[012C6FF0]: AVAILABLE: 1
device[012C6FF0]: COMPILER_AVAILABLE: 1
hello world 示例的结果是：计算出“0/1024”正确值！ 左右变化，所以它不会将结果比较为
result[i] == data[i]*data[i]
但是
(result[i] - data[i]*data[i] ) < 10e-6
我得到了正确的所有值。我现在想知道原因。所有数据都存储在主机上：
float data[DATA_SIZE]; // original data set given to device
float results[DATA_SIZE]; // results returned from device
我正在使用 Visual Studio 2010 进行编译，想知道如何评估两个浮点数 a == b，它需要相等的精度。
我是否应该始终假设我的 GPU 上的计算对于差异
最后，如果有人有一些非常好的入门指南，我很感兴趣。
【问题讨论】：
【参考方案1】：这是这个问题的一个很好的答案。
总结：cpu在做中间运算的时候，把80bit精度比float（32bit）高的值存储为result[i]
OpenCL Floating point precision
【讨论】：
【参考方案2】：何时：
result[i] == data[i]*data[i]
你计算了 data[i]*data[i]，然后存储在某个地方（临时变量、寄存器），然后与 result[i] 进行比较
何时：
result[i] - data[i]*data[i]
您已加载 data[i]，将其与自身相乘，然后减去 result[i]
在第一种情况下，您比较两个存储的浮点变量 在第二种情况下，您从存储的浮点数（具有固定的 4 字节表示）中减去一个中间计算结果（使用比存储表示更多的数字完成）。
在纯 cpu C++ 代码中您可能会得到相同的错误结果（可能因编译器/CPU 而异）。 公式中的任何中间结果都可以具有比数据类型更重要的数字，使用硬件精度，以便仅在存储结果时进行舍入。它提高了精度。
如果您想比较两者，请执行以下操作：
float a = result[i];
float b = data[i]*data[i];
float delta = a-b; // should be 0.0
通常，最好的做法是永远不要使用相等 (a == b) 来比较浮点值，原因太多了，因为这篇文章的篇幅太大。
在您的情况下，这是合法的（检查 GPU 和 CPU 上的精度/舍入是否相同），但只能比较存储的值
【讨论】：
【参考方案3】：没有绝对值可用于比较适用于所有情况的两个浮点数（任何精度）。原因是，由于表示，两个“相邻”浮点数可以有很大的绝对差异。更好的方法是使用相对误差进行比较（相对误差：abs((a-b)/b)）——虽然这只是一种粗略的方法，但您还需要考虑一些边缘情况。
阅读article和article了解更多信息
【讨论】：
我的代码中没有包含 abs() 是一个错误。我将查看这些文章，但正在寻找比缺少 abs() 的信息。谢谢。以上是关于OpenCL 的精度，hello world 示例中的浮点比较的主要内容，如果未能解决你的问题，请参考以下文章
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