/* *****************************************************************************
 * libg1m/bcd.h -- BCD-encoded numbers manipulation.
 * Copyright (C) 2017 Thomas "Cakeisalie5" Touhey <thomas@touhey.fr>
 *
 * This file is part of libg1m.
 * libg1m is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 3.0 of the License,
 * or (at your option) any later version.
 *
 * libg1m 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with libg1m; if not, see <http://www.gnu.org/licenses/>.
 *
 * BCD are the main number format CASIO uses in its calculators.
 * This format has the huge advantage to make 0.1 + 0.2 and 0.3 equal.
 *
 * There are several raw BCD formats, libg1m offers conversion to its own
 * format, easier to read and write (but not optimized for storing).
 * ************************************************************************** */
#ifndef LIBG1M_BCD_H
# define LIBG1M_BCD_H
# ifdef __cplusplus
extern "C" {
# endif
# define G1M_BCD_MANTISSA_SIZE 16
# define G1M_BCD_EXPMIN -99
# define G1M_BCD_EXPMAX  99

/* String constants; here are some examples:
 * - 1.23456789ABCDEFe99
 * - -0.0000123456789ABCDEF
 * - 123456789ABCDEF0000000 */

# define G1M_BCD_GOODBUFSIZE \
	(2 + G1M_BCD_MANTISSA_SIZE + 4 + 2 + 1)

/* ************************************************************************** */
/*  Main type                                                                 */
/* ************************************************************************** */
/* libg1m type definition
 * This is the "unzipped" BCD format. There are several, this is the one libg1m
 * will always convert to.
 *
 * `flags` is the flags (negative, special, precision) of the BCD.
 * `exp` is the 10-exponent, between -99 and 99.
 * `mant` is the mantissa: unpacked BCD digits (one digit per byte).
 *
 * The first digit of the mantissa is the integer part, the others are
 * the decimal part.
 *
 * To interact the flags or the exponent, it is advised to use the g1m_bcd_*
 * macros, as some of them could change. */

# define g1m_bcdflag_spe 0x80
# define g1m_bcdflag_neg 0x40
# define g1m_bcdmask_pre 0x3F

# define g1m_bcd_has_special(B) ((B)->flags & g1m_bcdflag_spe)
# define g1m_bcd_is_negative(B) ((B)->flags & g1m_bcdflag_neg)
# define g1m_bcd_precision(B)   ((B)->flags & g1m_bcdmask_pre)
# define g1m_bcd_exponent(B)    ((B)->exp)
# define g1m_make_bcdflags(SPE, NEG, PREC) \
	(((SPE) << 7) | ((NEG) << 6) | (PREC))

typedef struct g1m_bcd_s {
	unsigned char flags; char exp;
	char mant[G1M_BCD_MANTISSA_SIZE];
} g1m_bcd_t;

/* ************************************************************************** */
/*  Raw formats                                                               */
/* ************************************************************************** */
/* CAS BCD -- the old BCD format.
 *
 * First two nibbles are the integer part, the fourteen that follow are
 * the decimal part. They are followed by the sign info byte, then with a
 * BCD exponent (two nibbles).
 *
 * The sign info byte is basically the flags of the number.
 * The negative is two bits/flags (I don't know why).
 * `g1m_casbcd_pow_neg`, if there, means the power is negative. */

# define g1m_casbcd_special  0x80
# define g1m_casbcd_negative 0x50
# define g1m_casbcd_pow_neg  0x01
typedef struct {
	unsigned char mantissa[8];
	unsigned char signinfo;
	unsigned char exponent;
} cas_bcd_t;

/* MCS BCD -- the most recent BCD format.
 * Only the first 9 bytes are significant.
 *
 * The highest bit of the first byte isn't to be considered as part of the
 * first nibble, it means something else (generally "the number has a complex
 * part").
 *
 * The first three nibbles are the exponent. If it is more than 500, the
 * number is negative. Its offset is -99.
 * The other values (from the fourth nibble) are the packed BCD mantissa.
 * It starts at 10^0. */

typedef struct bcd {
	unsigned char BCDval[9];
	unsigned char _align[3];
} mcs_bcd_t;

/* ************************************************************************** */
/*  Conversion utilities                                                      */
/* ************************************************************************** */
/* From and to MCS BCD. */
int g1m_bcd_frommcs(const mcs_bcd_t *raw, g1m_bcd_t *bcd);
void  g1m_bcd_tomcs(const g1m_bcd_t *bcd, mcs_bcd_t *raw);

/* From and to CAS BCD. */
int g1m_bcd_fromcas(const cas_bcd_t *raw, g1m_bcd_t *bcd);
void  g1m_bcd_tocas(const g1m_bcd_t *bcd, cas_bcd_t *raw);

/* From and to C-double */
void g1m_bcd_fromdouble(double dbl, g1m_bcd_t *bcd);
double g1m_bcd_todouble(const g1m_bcd_t *bcd);

/* Make a string out of a BCD */
size_t g1m_bcdtoa(const g1m_bcd_t *bcd, char *buf, size_t len);

# ifdef __cplusplus
}
# endif
#endif /* LIBG1M_BCD_H */