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Compiler Reference Guide

Conventions and Feedback Introduction Compiler Command-line Options Language Extensions Compiler-specific Features Keywords and operators __align __alignof__ __ALIGNOF__ __asm __forceinline __global_reg __inline __int64 __INTADDR__ __irq __packed __pure __smc __softfp __svc __svc_indirect __svc_indirect_r7 __value_in_regs __weak __writeonly __declspec attributes __declspec(dllexport) __declspec(dllimport) __declspec(noinline) __declspec(noreturn) __declspec(nothrow) __declspec(notshared) __declspec(thread) Function attributes __attribute__((alias)) function attribute __attribute__((always_inline)) function attribute __attribute__((const)) function attribute __attribute__((constructor[(priority)])) function __attribute__((deprecated)) function attribute __attribute__((destructor[(priority)])) function a __attribute__((format_arg(string-index))) function __attribute__((malloc)) function attribute __attribute__((noinline)) function attribute __attribute__((nomerge)) function attribute __attribute__((nonnull)) function attribute __attribute__((noreturn)) function attribute __attribute__((notailcall)) function attribute __attribute__((pcs("calling_convention") __attribute__((pure)) function attribute __attribute__((section("name"))) functio __attribute__((unused)) function attribute __attribute__((used)) function attribute __attribute__((visibility("visibility_type&qu __attribute__((weak)) function attribute __attribute__((weakref("target"))) funct Type attributes __attribute__((bitband)) type attribute __attribute__((aligned)) type attribute __attribute((packed)) type attribute __attribute__((transparent_union)) type attribute Variable attributes __attribute__((alias)) variable attribute __attribute__((at(address))) variable attribute __attribute__((aligned)) variable attribute __attribute__((deprecated)) variable attribute __attribute__((noinline)) constant variable attrib __attribute__((packed)) variable attribute __attribute__((section("name"))) variabl __attribute__((transparent_union)) variable attrib __attribute__((unused)) variable attribute __attribute__((used)) variable attribute __attribute__((visibility("visibility_type&qu __attribute__((weak)) variable attribute __attribute__((weakref("target"))) varia __attribute__((zero_init)) variable attribute Pragmas #pragma anon_unions, #pragma no_anon_unions #pragma arm #pragma arm section [section_type_list] #pragma diag_default tag[,tag,...] #pragma diag_error tag[,tag,...] #pragma diag_remark tag[,tag,...] #pragma diag_suppress tag[,tag,...] #pragma diag_warning tag[, tag, ...] #pragma exceptions_unwind, #pragma no_exceptions_u #pragma hdrstop #pragma import symbol_name #pragma import(__use_full_stdio) #pragma import(__use_smaller_memcpy) #pragma inline, #pragma no_inline #pragma no_pch #pragma Onum #pragma once #pragma Ospace #pragma Otime #pragma pack(n) #pragma pop #pragma push #pragma softfp_linkage, #pragma no_softfp_linkage #pragma thumb #pragma unroll [(n)] #pragma unroll_completely #pragma weak symbol, #pragma weak symbol1 = symbol Instruction intrinsics __breakpoint intrinsic __cdp intrinsic __clrex intrinsic __clz intrinsic __current_pc intrinsic __current_sp intrinsic __disable_fiq intrinsic __disable_irq intrinsic __enable_fiq intrinsic __enable_irq intrinsic __fabs intrinsic __fabsf intrinsic __force_stores intrinsic __ldrex intrinsic __ldrexd intrinsic __ldrt intrinsic __memory_changed intrinsic __nop intrinsic __pld intrinsic __pldw intrinsic __pli intrinsic __promise intrinsic __qadd intrinsic __qdbl intrinsic __qsub intrinsic __rbit intrinsic __rev intrinsic __return_address intrinsic __ror intrinsic __schedule_barrier intrinsic __semihost intrinsic __sev intrinsic __sqrt intrinsic __sqrtf intrinsic __ssat intrinsic __strex intrinsic __strexd intrinsic __strt intrinsic __swp intrinsic __usat intrinsic __wfe intrinsic __wfi intrinsic __yield intrinsic ARMv6 SIMD intrinsics ETSI basic operations C55x intrinsics VFP status intrinsic __vfp_status intrinsic Fused Multiply Add (FMA) intrinsics Named register variables Predefined macros Built-in function name variables C and C++ Implementation Details Semihosting ARMv6 SIMD Instruction Intrinsics Via File Syntax Standard C Implementation Definition Standard C++ Implementation Definition C and C++ Compiler Implementation Limits
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__attribute__((const)) function attribute

ARM Compiler toolchain v5.02 for µVision Compiler Reference
Home > Compiler-specific Features > __attribute__((const)) function attribute

__attribute__((const)) function attribute

Many functions examine only the arguments passed to them, and have no effects except for the return value. This is a much stricter class than __attribute__((pure)), because a function is not permitted to read global memory. If a function is known to operate only on its arguments then it can be subject to common sub-expression elimination and loop optimizations.

Note

This function attribute is a GNU compiler extension that the ARM compiler supports. It has the keyword equivalent __pure.

Show/hideExample

int Function_Attributes_const_0(int b) __attribute__((const));
int Function_Attributes_const_0(int b)
{
    int aLocal=0;
    aLocal += Function_Attributes_const_0(b);
    aLocal += Function_Attributes_const_0(b);
    return aLocal;
}

In this code Function_Attributes_const_0 might be called once only, with the result being doubled to obtain the correct return value.

Show/hideSee also

Copyright © 2007-2008, 2011-2012 ARM. All rights reserved.ARM DUI 0376D
Non-ConfidentialID062912
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Home > Compiler-specific Features > __attribute__((const)) function attribute

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