ARM + iOS instructions
git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@715 632fc199-4ca6-4c93-a231-07263d6284db
diff --git a/BUILDING.txt b/BUILDING.txt
index 8279ec6..533d535 100644
--- a/BUILDING.txt
+++ b/BUILDING.txt
@@ -11,7 +11,7 @@
-- automake 1.7 or later
-- libtool 1.4 or later
--- NASM
+-- NASM (if building x86 or x86-64 SIMD extensions)
* 0.98, or 2.01 or later is required for a 32-bit build
* NASM 2.00 or later is required for a 64-bit build
* NASM 2.07 or later is required for a 64-bit build on OS X. This can be
@@ -281,6 +281,55 @@
Use CMake (see recipes below)
+===========
+ARM Support
+===========
+
+This release of libjpeg-turbo can use ARM NEON SIMD instructions to accelerate
+JPEG compression/decompression by approximately 2-4x on ARMv7 and later
+platforms. If libjpeg-turbo is configured on an ARM Linux platform, then the
+build system will automatically include the NEON SIMD routines, if they are
+supported.
+
+
+Building libjpeg-turbo for iOS
+------------------------------
+
+iOS platforms, such as the iPhone and iPad, also use ARM processors, some of
+which support NEON instructions. Additional steps are required to build
+libjpeg-turbo for these platforms. The steps below assume iOS SDK v4.3. If
+you are using a different SDK version, then you will need to modify the
+examples accordingly.
+
+Additional build requirements:
+
+ gas-preprocessor.pl (https://github.com/yuvi/gas-preprocessor) should be
+ installed in your PATH.
+
+Set the following shell variables for simplicity:
+
+ IOS_PLATFORMDIR="/Developer/Platforms/iPhoneOS.platform"
+ IOS_SYSROOT="$IOS_PLATFORMDIR/Developer/SDKs/iPhoneOS4.3.sdk"
+ IOS_GCC="$IOS_PLATFORMDIR/Developer/usr/bin/arm-apple-darwin10-llvm-gcc-4.2"
+
+ ARM v6 only (up to and including iPhone 3G):
+ IOS_CFLAGS="-march=armv6 -mcpu=arm1176jzf-s -mfpu=vfp"
+
+ ARM v7 only (iPhone 3GS and newer, iPad):
+ IOS_CFLAGS="-march=armv7 -mcpu=cortex-a8 -mtune=cortex-a8 -mfpu=neon"
+
+Follow the procedure under "Building libjpeg-turbo" above, adding
+
+ --host arm-apple-darwin10 \
+ CC="$IOS_GCC" LD="$IOS_GCC" \
+ CFLAGS="-mfloat-abi=softfp -isysroot $IOS_SYSROOT -O3 $IOS_CFLAGS" \
+ LDFLAGS="-mfloat-abi=softfp -isysroot $IOS_SYSROOT $IOS_CFLAGS"
+
+to the configure command line.
+
+Once built, lipo can be used to combine the ARM v6 and v7 variants into a
+universal library.
+
*******************************************************************************
** Building on Windows (Visual C++ or MinGW)