// SPDX-License-Identifier: LGPL-3.0-or-later

/**
 * \file numlib_fltp.h
 *
 * Lookup table and function to `#include`d in `numlib_ftoa.c`.
 *
 * \copyright The DoubleFourteen Code Forge (C) All Rights Reserved
 * \author    Lorenzo Cogotti
 */

#define npowers     87
#define steppowers  8
#define firstpower -348  // 10 ^ -348

#define expmax     -32
#define expmin     -60

typedef struct {
	Uint64 frac;
	int    exp;
} Fp;

static const Fp powers_ten[] = {
	{ 18054884314459144840uLL, -1220 }, { 13451937075301367670uLL, -1193 },
	{ 10022474136428063862uLL, -1166 }, { 14934650266808366570uLL, -1140 },
	{ 11127181549972568877uLL, -1113 }, { 16580792590934885855uLL, -1087 },
	{ 12353653155963782858uLL, -1060 }, { 18408377700990114895uLL, -1034 },
	{ 13715310171984221708uLL, -1007 }, { 10218702384817765436uLL, -980 },
	{ 15227053142812498563uLL, -954 },  { 11345038669416679861uLL, -927 },
	{ 16905424996341287883uLL, -901 },  { 12595523146049147757uLL, -874 },
	{ 9384396036005875287uLL,  -847 },  { 13983839803942852151uLL, -821 },
	{ 10418772551374772303uLL, -794 },  { 15525180923007089351uLL, -768 },
	{ 11567161174868858868uLL, -741 },  { 17236413322193710309uLL, -715 },
	{ 12842128665889583758uLL, -688 },  { 9568131466127621947uLL,  -661 },
	{ 14257626930069360058uLL, -635 },  { 10622759856335341974uLL, -608 },
	{ 15829145694278690180uLL, -582 },  { 11793632577567316726uLL, -555 },
	{ 17573882009934360870uLL, -529 },  { 13093562431584567480uLL, -502 },
	{ 9755464219737475723uLL,  -475 },  { 14536774485912137811uLL, -449 },
	{ 10830740992659433045uLL, -422 },  { 16139061738043178685uLL, -396 },
	{ 12024538023802026127uLL, -369 },  { 17917957937422433684uLL, -343 },
	{ 13349918974505688015uLL, -316 },  { 9946464728195732843uLL,  -289 },
	{ 14821387422376473014uLL, -263 },  { 11042794154864902060uLL, -236 },
	{ 16455045573212060422uLL, -210 },  { 12259964326927110867uLL, -183 },
	{ 18268770466636286478uLL, -157 },  { 13611294676837538539uLL, -130 },
	{ 10141204801825835212uLL, -103 },  { 15111572745182864684uLL, -77 },
	{ 11258999068426240000uLL, -50 },   { 16777216000000000000uLL, -24 },
	{ 12500000000000000000uLL,   3 },   { 9313225746154785156uLL,   30 },
	{ 13877787807814456755uLL,  56 },   { 10339757656912845936uLL,  83 },
	{ 15407439555097886824uLL, 109 },   { 11479437019748901445uLL, 136 },
	{ 17105694144590052135uLL, 162 },   { 12744735289059618216uLL, 189 },
	{ 9495567745759798747uLL,  216 },   { 14149498560666738074uLL, 242 },
	{ 10542197943230523224uLL, 269 },   { 15709099088952724970uLL, 295 },
	{ 11704190886730495818uLL, 322 },   { 17440603504673385349uLL, 348 },
	{ 12994262207056124023uLL, 375 },   { 9681479787123295682uLL,  402 },
	{ 14426529090290212157uLL, 428 },   { 10748601772107342003uLL, 455 },
	{ 16016664761464807395uLL, 481 },   { 11933345169920330789uLL, 508 },
	{ 17782069995880619868uLL, 534 },   { 13248674568444952270uLL, 561 },
	{ 9871031767461413346uLL,  588 },   { 14708983551653345445uLL, 614 },
	{ 10959046745042015199uLL, 641 },   { 16330252207878254650uLL, 667 },
	{ 12166986024289022870uLL, 694 },   { 18130221999122236476uLL, 720 },
	{ 13508068024458167312uLL, 747 },   { 10064294952495520794uLL, 774 },
	{ 14996968138956309548uLL, 800 },   { 11173611982879273257uLL, 827 },
	{ 16649979327439178909uLL, 853 },   { 12405201291620119593uLL, 880 },
	{ 9242595204427927429uLL,  907 },   { 13772540099066387757uLL, 933 },
	{ 10261342003245940623uLL, 960 },   { 15290591125556738113uLL, 986 },
	{ 11392378155556871081uLL, 1013 },  { 16975966327722178521uLL, 1039 },
	{ 12648080533535911531uLL, 1066 }
};

static Fp find_cachedpow10(int exp, int *k)
{
	const double one_log_ten = 0.30102999566398114;

	int approx = -(exp + npowers) * one_log_ten;
	int idx    = (approx - firstpower) / steppowers;

	while (TRUE) {
		int current = exp + powers_ten[idx].exp + 64;

		if (current < expmin) {
			idx++;
			continue;
		}
		if (current > expmax) {
			idx--;
			continue;
		}

		*k = (firstpower + idx * steppowers);
		break;
	}

	return powers_ten[idx];
}