Functions for CPU features and intrinsics. More...

#include "config.h"

Macros
#define	NEW_LINE

#define	INTEL_PREFIX

#define	INTEL_NOPREFIX

#define	ATT_PREFIX

#define	ATT_NOPREFIX

#define	PERCENT_PASTE(x) "%" #x

#define	PERCENT_REG(x) PERCENT_PASTE(x)

Functions
int	GetCacheLineSize ()
	Provides the cache line size.

Detailed Description

Functions for CPU features and intrinsics.

The CPU functions are used in IA-32, ARM and PowerPC code paths. The functions provide cpu specific feature testing on IA-32, ARM and PowerPC machines.

Feature detection uses CPUID on IA-32, like Intel and AMD. On other platforms a two-part strategy is used. First, the library attempts to Query the OS for a feature, like using Linux getauxval() or android_getCpuFeatures(). If that fails, then Probe the cpu executing an instruction and an observe a SIGILL if unsupported. The general pattern used by the library is:

   g_hasCRC32 = CPU_QueryCRC32() || CPU_ProbeCRC32();
   g_hasPMULL = CPU_QueryPMULL() || CPU_ProbePMULL();
   g_hasAES  = CPU_QueryAES() || CPU_ProbeAES();

Generally speaking, CPU_Query() is in the source file cpu.cpp because it does not require special architectural flags. CPU_Probe() is in a source file that receives architectural flags, like sse_simd.cpp, neon_simd.cpp and ppc_simd.cpp. For example, compiling neon_simd.cpp on an ARM64 machine will have -march=armv8-a applied during a compile to make the instruction set architecture (ISA) available.

The cpu probes are expensive when compared to a standard OS feature query. The library also avoids probes on Apple platforms because Apple's signal handling for SIGILLs appears to corrupt memory. CPU_Probe() will unconditionally return false for Apple platforms. OpenSSL experienced the same problem and moved away from SIGILL probes on Apple.

Definition in file cpu.h.

Macro Definition Documentation

◆ ATT_NOPREFIX

#define ATT_NOPREFIX

Definition at line 60 of file cpu.h.

◆ ATT_PREFIX

#define ATT_PREFIX

Definition at line 59 of file cpu.h.

◆ INTEL_NOPREFIX

#define INTEL_NOPREFIX

Definition at line 58 of file cpu.h.

◆ INTEL_PREFIX

#define INTEL_PREFIX

Definition at line 57 of file cpu.h.

◆ NEW_LINE

#define NEW_LINE

Definition at line 56 of file cpu.h.

◆ PERCENT_PASTE

#define PERCENT_PASTE ( x ) "%" #x

Definition at line 64 of file cpu.h.

◆ PERCENT_REG

#define PERCENT_REG ( x ) PERCENT_PASTE(x)

Definition at line 65 of file cpu.h.

Function Documentation

◆ GetCacheLineSize()

int GetCacheLineSize ( )

inline

Provides the cache line size.

Returns: lower bound on the size of a cache line in bytes, if available

GetCacheLineSize() returns the lower bound on the size of a cache line, if it is available. If the value is not available at runtime, then 32 is returned for a 32-bit processor and 64 is returned for a 64-bit processor.

x86/x32/x64 uses CPUID to determine the value and it is usually accurate. PowerPC and AIX also makes the value available to user space and it is also usually accurate. The ARM processor equivalent is a privileged instruction, so a compile time value is returned.

Definition at line 889 of file cpu.h.

Macros

Functions