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-rw-r--r--src/lib/exchange_api_stefan.c320
1 files changed, 0 insertions, 320 deletions
diff --git a/src/lib/exchange_api_stefan.c b/src/lib/exchange_api_stefan.c
deleted file mode 100644
index c3576cd73..000000000
--- a/src/lib/exchange_api_stefan.c
+++ /dev/null
@@ -1,320 +0,0 @@
-/*
- This file is part of TALER
- Copyright (C) 2023 Taler Systems SA
-
- TALER is free software; you can redistribute it and/or modify it under the
- terms of the GNU General Public License as published by the Free Software
- Foundation; either version 3, or (at your option) any later version.
-
- TALER is distributed in the hope that it will be useful, but WITHOUT ANY
- WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- A PARTICULAR PURPOSE. See the GNU General Public License for more details.
-
- You should have received a copy of the GNU General Public License along with
- TALER; see the file COPYING. If not, see
- <http://www.gnu.org/licenses/>
-*/
-/**
- * @file lib/exchange_api_stefan.c
- * @brief calculations on the STEFAN curve
- * @author Christian Grothoff
- */
-#include "platform.h"
-#include "taler_json_lib.h"
-#include <gnunet/gnunet_curl_lib.h>
-#include "exchange_api_handle.h"
-#include <math.h>
-
-
-/**
- * Determine smallest denomination in @a keys.
- *
- * @param keys exchange response to evaluate
- * @return NULL on error (no denominations)
- */
-static const struct TALER_Amount *
-get_unit (const struct TALER_EXCHANGE_Keys *keys)
-{
- const struct TALER_Amount *min = NULL;
-
- for (unsigned int i = 0; i<keys->num_denom_keys; i++)
- {
- const struct TALER_EXCHANGE_DenomPublicKey *dk
- = &keys->denom_keys[i];
-
- if ( (NULL == min) ||
- (1 == TALER_amount_cmp (min,
- /* > */
- &dk->value)) )
- min = &dk->value;
- }
- GNUNET_break (NULL != min);
- return min;
-}
-
-
-/**
- * Convert amount to double for STEFAN curve evaluation.
- *
- * @param a input amount
- * @return (rounded) amount as a double
- */
-static double
-amount_to_double (const struct TALER_Amount *a)
-{
- double d = (double) a->value;
-
- d += a->fraction / ((double) TALER_AMOUNT_FRAC_BASE);
- return d;
-}
-
-
-/**
- * Convert double to amount for STEFAN curve evaluation.
- *
- * @param dv input amount
- * @param currency deisred currency
- * @param[out] rval (rounded) amount as a double
- */
-static void
-double_to_amount (double dv,
- const char *currency,
- struct TALER_Amount *rval)
-{
- double rem;
-
- GNUNET_assert (GNUNET_OK ==
- TALER_amount_set_zero (currency,
- rval));
- rval->value = floorl (dv);
- rem = dv - ((double) rval->value);
- if (rem < 0.0)
- rem = 0.0;
- rem *= TALER_AMOUNT_FRAC_BASE;
- rval->fraction = floorl (rem);
- if (rval->fraction >= TALER_AMOUNT_FRAC_BASE)
- {
- /* Strange, multiplication overflowed our range,
- round up value instead */
- rval->fraction = 0;
- rval->value += 1;
- }
-}
-
-
-enum GNUNET_GenericReturnValue
-TALER_EXCHANGE_keys_stefan_b2n (
- const struct TALER_EXCHANGE_Keys *keys,
- const struct TALER_Amount *brut,
- struct TALER_Amount *net)
-{
- const struct TALER_Amount *min;
- double log_d = amount_to_double (&keys->stefan_log);
- double lin_d = keys->stefan_lin;
- double abs_d = amount_to_double (&keys->stefan_abs);
- double bru_d = amount_to_double (brut);
- double min_d;
- double fee_d;
- double net_d;
-
- if (TALER_amount_is_zero (brut))
- {
- *net = *brut;
- return GNUNET_NO;
- }
- min = get_unit (keys);
- if (NULL == min)
- return GNUNET_SYSERR;
- if (1.0f <= keys->stefan_lin)
- {
- /* This cannot work, linear STEFAN fee estimate always
- exceed any gross amount. */
- GNUNET_break_op (0);
- return GNUNET_SYSERR;
- }
- min_d = amount_to_double (min);
- fee_d = abs_d
- + log_d * log2 (bru_d / min_d)
- + lin_d * bru_d;
- if (fee_d > bru_d)
- {
- GNUNET_assert (GNUNET_OK ==
- TALER_amount_set_zero (brut->currency,
- net));
- return GNUNET_NO;
- }
- net_d = bru_d - fee_d;
- double_to_amount (net_d,
- brut->currency,
- net);
- return GNUNET_OK;
-}
-
-
-/**
- * Our function
- * f(x) := ne + ab + lo * log2(x/mi) + li * x - x
- * for #newton().
- */
-static double
-eval_f (double mi,
- double ab,
- double lo,
- double li,
- double ne,
- double x)
-{
- return ne + ab + lo * log2 (x / mi) + li * x - x;
-}
-
-
-/**
- * Our function
- * f'(x) := lo / log(2) / x + li - 1
- * for #newton().
- */
-static double
-eval_fp (double mi,
- double lo,
- double li,
- double ne,
- double x)
-{
- return lo / log (2) / x + li - 1;
-}
-
-
-/**
- * Use Newton's method to find x where f(x)=0.
- *
- * @return x where "eval_f(x)==0".
- */
-static double
-newton (double mi,
- double ab,
- double lo,
- double li,
- double ne)
-{
- const double eps = 0.00000001; /* max error allowed */
- double min_ab = ne + ab; /* result cannot be smaller than this! */
- /* compute lower bounds by various heuristics */
- double min_ab_li = min_ab + min_ab * li;
- double min_ab_li_lo = min_ab_li + log2 (min_ab_li / mi) * lo;
- double min_ab_lo = min_ab + log2 (min_ab / mi) * lo;
- double min_ab_lo_li = min_ab_lo + min_ab_lo * li;
- /* take global lower bound */
- double x_min = GNUNET_MAX (min_ab_lo_li,
- min_ab_li_lo);
- double x = x_min; /* use lower bound as starting point */
-
- /* Objective: invert
- ne := br - ab - lo * log2 (br/mi) - li * br
- to find 'br'.
- Method: use Newton's method to find root of:
- f(x) := ne + ab + lo * log2 (x/mi) + li * x - x
- using also
- f'(x) := lo / log(2) / x + li - 1
- */
- /* Loop to abort in case of divergence;
- 100 is already very high, 2-4 is normal! */
- for (unsigned int i = 0; i<100; i++)
- {
- double fx = eval_f (mi, ab, lo, li, ne, x);
- double fxp = eval_fp (mi, lo, li, ne, x);
- double x_new = x - fx / fxp;
-
- if (fabs (x - x_new) <= eps)
- {
- GNUNET_log (GNUNET_ERROR_TYPE_INFO,
- "Needed %u rounds from %f to result BRUT %f => NET: %f\n",
- i,
- x_min,
- x_new,
- x_new - ab - li * x_new - lo * log2 (x / mi));
- return x_new;
- }
- if (x_new < x_min)
- {
- GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
- "Divergence, obtained very bad estimate %f after %u rounds!\n",
- x_new,
- i);
- return x_min;
- }
- x = x_new;
- }
- GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
- "Slow convergence, returning bad estimate %f!\n",
- x);
- return x;
-}
-
-
-enum GNUNET_GenericReturnValue
-TALER_EXCHANGE_keys_stefan_n2b (
- const struct TALER_EXCHANGE_Keys *keys,
- const struct TALER_Amount *net,
- struct TALER_Amount *brut)
-{
- const struct TALER_Amount *min;
- double lin_d = keys->stefan_lin;
- double log_d = amount_to_double (&keys->stefan_log);
- double abs_d = amount_to_double (&keys->stefan_abs);
- double net_d = amount_to_double (net);
- double min_d;
- double brut_d;
-
- if (TALER_amount_is_zero (net))
- {
- *brut = *net;
- return GNUNET_NO;
- }
- min = get_unit (keys);
- if (NULL == min)
- return GNUNET_SYSERR;
- if (1.0f <= keys->stefan_lin)
- {
- /* This cannot work, linear STEFAN fee estimate always
- exceed any gross amount. */
- GNUNET_break_op (0);
- return GNUNET_SYSERR;
- }
- min_d = amount_to_double (min);
- brut_d = newton (min_d,
- abs_d,
- log_d,
- lin_d,
- net_d);
- double_to_amount (brut_d,
- net->currency,
- brut);
- return GNUNET_OK;
-}
-
-
-void
-TALER_EXCHANGE_keys_stefan_round (
- const struct TALER_EXCHANGE_Keys *keys,
- struct TALER_Amount *val)
-{
- const struct TALER_Amount *min;
- uint32_t mod = 1;
- uint32_t frac;
- uint32_t rst;
-
- min = get_unit (keys);
- if (NULL == min)
- return;
- frac = min->fraction;
- while (0 == frac % 10)
- {
- mod *= 10;
- frac /= 10;
- }
- rst = val->fraction % mod;
- if (rst < mod / 2)
- val->fraction -= rst;
- else
- val->fraction += mod - rst;
-}
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