/*-
 * Copyright (c) 2004 Lev Walkin <vlm@lionet.info>. All rights reserved.
 * Redistribution and modifications are permitted subject to BSD license.
 */
#include <REAL.h>
#include <INTEGER.h>
#include <stdlib.h>	/* for strtod(3) */
#include <math.h>
#include <errno.h>
#include <assert.h>

#undef	INT_MAX
#define	INT_MAX	((int)(((unsigned int)-1) >> 1))

#ifndef	INFINITY
#define	INFINITY	HUGE_VAL
#endif

#ifndef	NAN
static const double nan0;
#define	NAN	(nan0/nan0)
#endif

/*
 * REAL basic type description.
 */
static ber_tlv_tag_t asn1_DEF_REAL_tags[] = {
	(ASN_TAG_CLASS_UNIVERSAL | (9 << 2))
};
asn1_TYPE_descriptor_t asn1_DEF_REAL = {
	"REAL",
	asn_generic_no_constraint,
	INTEGER_decode_ber,	/* Implemented in terms of INTEGER type */
	INTEGER_encode_der,
	REAL_print,
	INTEGER_free,
	0, /* Use generic outmost tag fetcher */
	asn1_DEF_REAL_tags,
	sizeof(asn1_DEF_REAL_tags) / sizeof(asn1_DEF_REAL_tags[0]),
	asn1_DEF_REAL_tags,	/* Same as above */
	sizeof(asn1_DEF_REAL_tags) / sizeof(asn1_DEF_REAL_tags[0]),
	0,	/* Always in primitive form */
	0, 0,	/* No members */
	0	/* No specifics */
};

int
REAL_print(asn1_TYPE_descriptor_t *td, const void *sptr, int ilevel,
	asn_app_consume_bytes_f *cb, void *app_key) {
	const REAL_t *st = (const REAL_t *)sptr;
	char buf[128];
	double d;
	int ret;

	(void)td;	/* Unused argument */
	(void)ilevel;	/* Unused argument */

	if(!st)
		return cb("<absent>", 8, app_key);

	if(asn1_REAL2double(st, &d))
		return cb("<error>", 7, app_key);

	ret = snprintf(buf, sizeof(buf), "%f", d);
	if(ret < 0 || ret >= sizeof(buf))
		return cb("<error>", 7, app_key);

	return cb(buf, ret, app_key);
}

int
asn1_REAL2double(const REAL_t *st, double *dbl_value) {
	unsigned long octv;

	if(!st || !st->buf) {
		errno = EINVAL;
		return -1;
	}

	if(st->size == 0) {
		*dbl_value = 0;
		return 0;
	}

	octv = st->buf[0];	/* unsigned byte */

	switch(octv & 0xC0) {
	case 0x40:	/* X.690: 8.5.8 */
		/* "SpecialRealValue" */

		/* Be liberal in what you accept...
		if(st->size != 1) ...
		*/

		switch(st->buf[0]) {
		case 0x40:	/* 01000000: PLUS-INFINITY */
			*dbl_value = INFINITY;
			return 0;
		case 0x41:	/* 01000001: MINUS-INFINITY */
			*dbl_value = -INFINITY;
			return 0;
			/*
			 * The following cases are defined by
			 * X.690 Amendment 1 (10/03)
			 */
		case 0x42:	/* 01000010: NOT-A-NUMBER */
			*dbl_value = NAN;
			return 0;
		case 0x43:	/* 01000011: minus zero */
			*dbl_value = NAN;
			return 0;
		}

		errno = EINVAL;
		return -1;
	case 0x00: {	/* X.690: 8.5.6 */
		/*
		 * Decimal. NR{1,2,3} format.
		 */
		double d;

		assert(st->buf[st->size - 1] == 0); /* Security, vashu mat' */

		d = strtod((char *)st->buf, 0);
		if(finite(d)) {
			*dbl_value = d;
			return 0;
		} else {
			errno = ERANGE;
			return 0;
		}
	  }
	}

	/*
	 * Binary representation.
	 */
    {
	double m;
	int expval;		/* exponent value */
	unsigned int elen;	/* exponent value length, in octets */
	unsigned int scaleF;
	unsigned int baseF;
	uint8_t *ptr;
	uint8_t *end;
	int sign;

	switch((octv & 0x30) >> 4) {
	case 0x00: baseF = 1; break;	/* base 2 */
	case 0x01: baseF = 3; break;	/* base 8 */
	case 0x02: baseF = 4; break;	/* base 16 */
	default:
		/* Reserved field, can't parse now. */
		errno = EINVAL;
		return -1;
	}

	sign = (octv & 0x40);	/* bit 7 */
	scaleF = (octv & 0x0C) >> 2;	/* bits 4 to 3 */

	if(st->size <= (1 + (octv & 0x03))) {
		errno = EINVAL;
		return -1;
	}

	if((octv & 0x03) == 0x11) {
		/* 8.5.6.4, case d) */
		elen = st->buf[1];	/* unsigned binary number */
		if(elen == 0 || st->size <= (2 + elen)) {
			errno = EINVAL;
			return -1;
		}
		ptr = &st->buf[2];
	} else {
		elen = (octv & 0x03);
		ptr = &st->buf[1];
	}

	/* Fetch the multibyte exponent */
	expval = (int)(*(int8_t *)ptr);
	end = ptr + elen + 1;
	for(ptr++; ptr < end; ptr++)
		expval = (expval * 256) + *ptr;

	m = 0.0;	/* Initial mantissa value */

	/* Okay, the exponent is here. Now, what about mantissa? */
	end = st->buf + st->size;
	if(ptr < end) {
		for(; ptr < end; ptr++)
			m = scalbn(m, 8) + *ptr;
	}

	ASN_DEBUG("m=%.10f, scF=%d, bF=%d, expval=%d, ldexp()=%f, scalbn()=%f",
		m, scaleF, baseF, expval,
		ldexp(m, expval * baseF + scaleF),
		scalbn(m, scaleF) * pow(pow(2, baseF), expval)
	);

	/*
	 * (S * N * 2^F) * B^E
	 * Essentially:
	m = scalbn(m, scaleF) * pow(pow(2, base), expval);
	 */
	m = ldexp(m, expval * baseF + scaleF);
	if(finite(m)) {
		*dbl_value = sign ? -m : m;
	} else {
		errno = ERANGE;
		return -1;
	}

    } /* if(binary_format) */

	return 0;
}

/*
 * Assume IEEE 754 floating point: standard 64 bit double.
 * [1 bit sign]  [11 bits exponent]  [52 bits mantissa]
 */
int
asn1_double2REAL(REAL_t *st, double dbl_value) {
#ifdef	WORDS_BIGENDIAN		/* Known to be big-endian */
	int littleEndian = 0;
#else				/* need to test: have no explicit information */
	unsigned int LE = 1;
	int littleEndian = *(unsigned char *)&LE;
#endif
	uint8_t buf[16];	/* More than enough for 8-byte dbl_value */
	uint8_t dscr[sizeof(dbl_value)];	/* double value scratch pad */
	/* Assertion guards: won't even compile, if unexpected double size */
	char assertion_buffer1[9 - sizeof(dbl_value)] __attribute__((unused));
	char assertion_buffer2[sizeof(dbl_value) - 7] __attribute__((unused));
	uint8_t *ptr = buf;
	uint8_t *mstop;		/* Last byte of mantissa */
	unsigned int mval;	/* Value of the last byte of mantissa */
	unsigned int bmsign;	/* binary mask with sign */
	unsigned int buflen;
	unsigned int accum;
	int expval;

	if(!st) {
		errno = EINVAL;
		return -1;
	}

	expval = ilogb(dbl_value);

	if(expval == -INT_MAX	/* Also catches (dbl_value == 0) */
	|| expval == INT_MAX	/* catches finite() which catches isnan() */
	) {
		if(!st->buf || st->size < 2) {
			(void *)ptr = MALLOC(2);
			if(!ptr) return -1;
			st->buf = ptr;
		}
		/* fpclassify(3) is not portable yet */
		if(expval == -INT_MAX) {
			if(signbit(dbl_value)) {
				st->buf[0] = 0x80 | 0x40;
				st->buf[1] = 0;
				st->size = 2;
			} else {
				st->buf[0] = 0;	/* JIC */
				st->size = 0;
			}
		} else if(isinf(dbl_value)) {
			if(signbit(dbl_value)) {
				st->buf[0] = 0x41;	/* MINUS-INFINITY */
			} else {
				st->buf[0] = 0x40;	/* PLUS-INFINITY */
			}
			st->buf[1] = 0;
			st->size = 1;
		} else {
			st->buf[0] = 0x42;	/* NaN */
			st->buf[1] = 0;
			st->size = 1;
		}
		return 0;
	}

	if(littleEndian) {
		uint8_t *s = ((uint8_t *)&dbl_value) + sizeof(dbl_value) - 2;
		uint8_t *d;

		bmsign = 0x80 | ((s[1] >> 1) & 0x40);	/* binary mask & - */
		for(mstop = d = dscr; s >= (uint8_t *)&dbl_value; d++, s--) {
			*d = *s;
			if(*d) mstop = d;
		}
	} else {
		uint8_t *s = ((uint8_t *)&dbl_value) + 1;
		uint8_t *end = ((uint8_t *)&dbl_value) + sizeof(double);
		uint8_t *d;

		bmsign = 0x80 | ((s[-1] >> 1) & 0x40);	/* binary mask & - */
		for(mstop = d = dscr; s < end; d++, s++) {
			*d = *s;
			if(*d) mstop = d;
		}
	}

	/* Remove parts of the exponent, leave mantissa and explicit 1. */
	dscr[0] = 0x10 | (dscr[0] & 0x0f);

	/* Adjust exponent in a very unobvious way */
	expval -= 8 * ((mstop - dscr) + 1) - 4;

	/* This loop ensures DER conformance by forcing mantissa odd: 11.3.1 */
	mval = *mstop;
	if(mval && !(mval & 1)) {
		unsigned int shift_count = 1;
		unsigned int ishift;
		uint8_t *mptr;

		/*
		 * Figure out what needs to be done to make mantissa odd.
		 */
		if(!(mval & 0x0f))	/* Speed-up a little */
			shift_count = 4;
		while(((mval >> shift_count) & 1) == 0)
			shift_count++;

		ishift = 8 - shift_count;
		accum = 0;

		/* Go over the buffer, shifting it shift_count bits right. */
		for(mptr = dscr; mptr <= mstop; mptr++) {
			mval = *mptr;
			*mptr = accum | (mval >> shift_count);
			accum = mval << ishift;
		}

		/* Adjust mantissa appropriately. */
		expval += shift_count;
	}

	if(expval < 0) {
		if((expval >> 7) == -1) {
			*ptr++ = bmsign | 0x00;
			*ptr++ = expval;
		} else if((expval >> 15) == -1) {
			*ptr++ = bmsign | 0x01;
			*ptr++ = expval >> 8;
			*ptr++ = expval;
		} else {
			assert((expval >> 23) == -1);
			*ptr++ = bmsign | 0x02;
			*ptr++ = expval >> 16;
			*ptr++ = expval >> 8;
			*ptr++ = expval;
		}
	} else if(expval <= 0x7f) {
		*ptr++ = bmsign | 0x00;
		*ptr++ = expval;
	} else if(expval <= 0x7fff) {
		*ptr++ = bmsign | 0x01;
		*ptr++ = expval >> 8;
		*ptr++ = expval;
	} else {
		assert(expval <= 0x7fffff);
		*ptr++ = bmsign | 0x02;
		*ptr++ = expval >> 16;
		*ptr++ = expval >> 8;
		*ptr++ = expval;
	}

	buflen = (mstop - dscr) + 1;
	memcpy(ptr, dscr, buflen);
	ptr += buflen;
	buflen = ptr - buf;

	(void *)ptr = MALLOC(buflen + 1);
	if(!ptr) return -1;

	memcpy(ptr, buf, buflen);
	buf[buflen] = 0;	/* JIC */

	if(st->buf) FREEMEM(st->buf);
	st->buf = ptr;
	st->size = buflen;

	return 0;
}