# $Copyright:
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# This confidential and proprietary software may be used only as
# authorised by a licensing agreement from ARM Limited
# (C) COPYRIGHT 2000,2002 ARM Limited
# ALL RIGHTS RESERVED
# The entire notice above must be reproduced on all authorised
# copies and copies may only be made to the extent permitted
# by a licensing agreement from ARM Limited.
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# File: readme.txt,v
# Revision: 1.4
# ----------------------------------------------------------------
# $
!!! To fully understand the FFT/ARM9E/WIN_MOB implementation in SPLIB,
!!! you have to refer to the full set of files in RVDS' package:
!!! C:\Program Files\ARM\RVDS\Examples\3.0\79\windows\fft_v5te.
ARM Assembler FFT implementation
================================
Overview
========
This implementation has been restructured to allow FFT's of varying radix
rather than the fixed radix-2 or radix-4 versions allowed earlier. The
implementation of an optimised assembler FFT of a given size (N points)
consists of chaining together a sequence of stages 1,2,3,...,k such that the
j'th stage has radix Rj and:
N = R1*R2*R3*...*Rk
For the ARM implementations we keep the size of the Rj's decreasing with
increasing j, EXCEPT that if there are any non power of 2 factors (ie, odd
prime factors) then these come before all the power of 2 factors.
For example:
N=64 would be implemented as stages:
radix 4, radix 4, radix 4
N=128 would be implemented as stages:
radix 8, radix 4, radix 4
OR
radix 4, radix 4, radix 4, radix 2
N=192 would be implemented as stages:
radix 3, radix 4, radix 4, radix 4
The bitreversal is usally combined with the first stage where possible.
Structure
=========
The actual FFT routine is built out of a hierarchy of macros. All stage
macros and filenames are one of:
fs_rad<n> => the macro implements a radix <n> First Stage (usually
including the bit reversal)
gs_rad<n> => the macro implements a radix <n> General Stage (any
stage except the first - includes the twiddle operations)
ls_rad<n> => the macro implements a radix <n> Last Stage (this macro
is like the gs_rad<n> version but is optimised for
efficiency in the last stage)
ls_ztor => this macro converts the output of a complex FFT to
be the first half of the output of a real FFT of
double the number of input points.
Other files are:
fft_mac.h => Macro's and register definitions shared by all radix
implementations
fft_main.h => Main FFT macros drawing together the stage macros
to produce a complete FFT
Interfaces
==========
The register interfaces for the different type of stage macros are described
at the start of fft_mac.h
