d63d8364cf
In migrating towards using the newer functions scaled_div/scaled_div32 for TFRC computations mapped from floating-point onto integer arithmetic, this completes the last stage of modifications. In particular, the overflow case for computing X_calc is circumvented by * breaking the computation into two stages * the first stage, res = (s*1E6)/R, cannot overflow due to use of u64 * in the second stage, res = (res*1E6)/f, overflow on u32 is avoided due to (i) returning UINT_MAX in this case (which is logically appropriate) and (ii) issuing a warning message into the system log (since very likely there is a problem somewhere else with the parameters) Lastly, all such scaling operations are now exported into tfrc.h, since actually this form of scaled computation is specific to TFRC and not to CCID3. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
44 lines
1.1 KiB
C
44 lines
1.1 KiB
C
#ifndef _TFRC_H_
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#define _TFRC_H_
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/*
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* net/dccp/ccids/lib/tfrc.h
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*
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* Copyright (c) 2005 The University of Waikato, Hamilton, New Zealand.
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* Copyright (c) 2005 Ian McDonald <ian.mcdonald@jandi.co.nz>
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* Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
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* Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*/
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#include <linux/types.h>
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#include <asm/div64.h>
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/* integer-arithmetic divisions of type (a * 1000000)/b */
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static inline u64 scaled_div(u64 a, u32 b)
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{
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BUG_ON(b==0);
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a *= 1000000;
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do_div(a, b);
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return a;
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}
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static inline u32 scaled_div32(u64 a, u32 b)
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{
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u64 result = scaled_div(a, b);
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if (result > UINT_MAX) {
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DCCP_CRIT("Overflow: a(%llu)/b(%u) > ~0U",
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(unsigned long long)a, b);
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return UINT_MAX;
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}
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return result;
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}
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extern u32 tfrc_calc_x(u16 s, u32 R, u32 p);
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extern u32 tfrc_calc_x_reverse_lookup(u32 fvalue);
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#endif /* _TFRC_H_ */
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