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Technical Support
On-Line Manuals
Compiler User Guide
Preface
Overview of the Compiler
Getting Started with the Compiler
Compiler Features
Compiler intrinsics
Performance benefits of compiler intrinsics
ARM assembler instruction intrinsics
Generic intrinsics
Compiler intrinsics for controlling IRQ and FIQ in
Compiler intrinsics for inserting optimization bar
Compiler intrinsics for inserting native instructi
Compiler intrinsics for Digital Signal Processing
Compiler support for European Telecommunications S
Overflow and carry status flags for C and C++ code
Texas Instruments (TI) C55x intrinsics for optimiz
Compiler support for accessing registers using nam
Pragmas recognized by the compiler
Compiler and processor support for bit-banding
Compiler type attribute, __attribute__((bitband))
--bitband compiler command-line option
How the compiler handles bit-band objects placed o
Compiler support for thread-local storage
Compiler support for literal pools
Compiler eight-byte alignment features
Precompiled Header (PCH) files
Automatic Precompiled Header (PCH) file processing
Precompiled Header (PCH) file processing and the h
Precompiled Header (PCH) file creation requirement
Compilation with multiple Precompiled Header (PCH)
Obsolete Precompiled Header (PCH) files
Manually specifying the filename and location of a
Selectively applying Precompiled Header (PCH) file
Suppressing Precompiled Header (PCH) file processi
Message output during Precompiled Header (PCH) pro
Performance issues with Precompiled Header (PCH) f
Default compiler options that are affected by opti
Compiler Coding Practices
Compiler Diagnostic Messages
Using the Inline and Embedded Assemblers of the AR
Compiler Command-line Options
Language Extensions
Compiler-specific Features
C and C++ Implementation Details
What is Semihosting?
Via File Syntax
Summary Table of GNU Language Extensions
Standard C Implementation Definition
Standard C++ Implementation Definition
C and C++ Compiler Implementation Limits
Compiler intrinsics
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3.1 Compiler intrinsics
Compiler intrinsics are functions provided by the compiler. They enable you to easily incorporate domain-specific operations in C and C++ source code without resorting to complex implementations in assembly language.
The C and C++ languages are suited to a wide variety of tasks
but they do not provide in-built support for specific areas of application,
for example, Digital Signal Processing (DSP).
Within a given application domain, there is usually a range
of domain-specific operations that have to be performed frequently.
However, often these operations cannot be efficiently implemented
in C or C++. A typical example is the saturated add of two 32-bit
signed two’s complement integers, commonly used in DSP programming. The following example shows a C implementation of saturated add
operation
#include <limits.h>
int L_add(const int a, const int b)
{
int c;
c = a + b;
if (((a ^ b) & INT_MIN) == 0)
{
if ((c ^ a) & INT_MIN)
{
c = (a < 0) ? INT_MIN : INT_MAX;
}
}
return c;
}
Using compiler intrinsics, you can achieve
more complete coverage of target architecture instructions than
you would from the instruction selection of the compiler.
An intrinsic function has the appearance of a function call
in C or C++, but is replaced during compilation by a specific sequence
of low-level instructions. When implemented using an intrinsic,
for example, the saturated add function previous example has the form:
#include <dspfns.h> /* Include ETSI intrinsics */ ... int a, b, result; ... result = L_add(a, b); /* Saturated add of a and b */
Related concepts
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