Mercurial > public > ostc4
view Discovery/Src/crcmodel.c @ 250:822416168585 bm-2
Buelmann: new implementation for ceiling
Since my first functional fix in the ceiling computation in
commit ceecabfddb57, I noticed that the computation used a
linear search, that became rather computational expensive after
that commit. The simple question is: why not a binary search?
So, this commit implements the binary search. But there is a long
story attached to this. Comparing ceiling results from hwOS and this
OSTC4 code were very different. Basically, the original OSTC4
algorithm computed the ceiling using the same GFlow to GFhigh
slope, in such a way, that the ceiling was in sync with the
presented deco stops, where the hwOS code presents a GFhigh
based ceiling.
This said, it is more logical when the OSTC4 and hwOS code give
similar results. This new recursive algorithm gives very similar
results for the ceiling compared to hwOS.
To be complete here, the Buelmann ceiling is the depth to which
you can ascend, so that the leading tissue reaches GFhigh. This
also explains why the deepest deco stop is normally deeper than
the ceiling (unless one dives with GF like 80/80).
The code implemented here is rather straightforward recursion.
Signed-off-by: Jan Mulder <jlmulder@xs4all.nl>
author | Jan Mulder <jlmulder@xs4all.nl> |
---|---|
date | Thu, 11 Apr 2019 17:48:48 +0200 |
parents | 5f11787b4f42 |
children |
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/******************************************************************************/ /* Start of crcmodel.c */ /******************************************************************************/ /* */ /* Author : Ross Williams (ross@guest.adelaide.edu.au.). */ /* Date : 3 June 1993. */ /* Status : Public domain. */ /* */ /* Description : This is the implementation (.c) file for the reference */ /* implementation of the Rocksoft^tm Model CRC Algorithm. For more */ /* information on the Rocksoft^tm Model CRC Algorithm, see the document */ /* titled "A Painless Guide to CRC Error Detection Algorithms" by Ross */ /* Williams (ross@guest.adelaide.edu.au.). This document is likely to be in */ /* "ftp.adelaide.edu.au/pub/rocksoft". */ /* */ /* Note: Rocksoft is a trademark of Rocksoft Pty Ltd, Adelaide, Australia. */ /* */ /******************************************************************************/ /* */ /* Implementation Notes */ /* -------------------- */ /* To avoid inconsistencies, the specification of each function is not echoed */ /* here. See the header file for a description of these functions. */ /* This package is light on checking because I want to keep it short and */ /* simple and portable (i.e. it would be too messy to distribute my entire */ /* C culture (e.g. assertions package) with this package. */ /* */ /******************************************************************************/ #include "crcmodel.h" /******************************************************************************/ /* The following definitions make the code more readable. */ #define BITMASK(X) (1L << (X)) #define MASK32 0xFFFFFFFFL #define LOCAL static /******************************************************************************/ LOCAL ulong reflect P_((ulong v,int b)); LOCAL ulong reflect (ulong v,int b) /* Returns the value v with the bottom b [0,32] bits reflected. */ /* Example: reflect(0x3e23L,3) == 0x3e26 */ { int i; ulong t = v; for (i=0; i<b; i++) { if (t & 1L) v|= BITMASK((b-1)-i); else v&= ~BITMASK((b-1)-i); t>>=1; } return v; } /******************************************************************************/ LOCAL ulong widmask P_((p_cm_t)); LOCAL ulong widmask (p_cm_t p_cm) /* Returns a longword whose value is (2^p_cm->cm_width)-1. */ /* The trick is to do this portably (e.g. without doing <<32). */ { return (((1L<<(p_cm->cm_width-1))-1L)<<1)|1L; } /******************************************************************************/ void cm_ini (p_cm_t p_cm) { p_cm->cm_reg = p_cm->cm_init; } /******************************************************************************/ void cm_nxt (p_cm_t p_cm, int ch) { int i; ulong uch = (ulong) ch; ulong topbit = BITMASK(p_cm->cm_width-1); if (p_cm->cm_refin) uch = reflect(uch,8); p_cm->cm_reg ^= (uch << (p_cm->cm_width-8)); for (i=0; i<8; i++) { if (p_cm->cm_reg & topbit) p_cm->cm_reg = (p_cm->cm_reg << 1) ^ p_cm->cm_poly; else p_cm->cm_reg <<= 1; p_cm->cm_reg &= widmask(p_cm); } } /******************************************************************************/ void cm_blk (p_cm_t p_cm,p_ubyte_ blk_adr,ulong blk_len) { while (blk_len--) cm_nxt(p_cm,*blk_adr++); } /******************************************************************************/ ulong cm_crc (p_cm_t p_cm) { if (p_cm->cm_refot) return p_cm->cm_xorot ^ reflect(p_cm->cm_reg,p_cm->cm_width); else return p_cm->cm_xorot ^ p_cm->cm_reg; } /******************************************************************************/ ulong cm_tab (p_cm_t p_cm, int index) { int i; ulong r; ulong topbit = BITMASK(p_cm->cm_width-1); ulong inbyte = (ulong) index; if (p_cm->cm_refin) inbyte = reflect(inbyte,8); r = inbyte << (p_cm->cm_width-8); for (i=0; i<8; i++) if (r & topbit) r = (r << 1) ^ p_cm->cm_poly; else r<<=1; if (p_cm->cm_refin) r = reflect(r,p_cm->cm_width); return r & widmask(p_cm); } /******************************************************************************/ /* End of crcmodel.c */ /******************************************************************************/