/**********************************************************************
*
* atof util
*
* Copyright (c) 2019 Dario Deledda. All rights reserved.
* Use of this source code is governed by an MIT license
* that can be found in the LICENSE file.
*
* This file contains utilities for convert a string in a f64 variable
* IEEE 754 standard is used
*
* Know limitation:
* - limited to 18 significant digits
*
* The code is inspired by:
* Grzegorz Kraszewski krashan@teleinfo.pb.edu.pl
* URL: http://krashan.ppa.pl/articles/stringtofloat/
* Original license: MIT
*
**********************************************************************/
module strconv

/**********************************************************************
*
* 96 bit operation utilities
* Note: when u128 will be available these function can be refactored
*
**********************************************************************/
// right logical shift 96 bit
fn lsr96(s2 u32, s1 u32, s0 u32) (u32, u32, u32) {
	mut r0 := u32(0)
	mut r1 := u32(0)
	mut r2 := u32(0)
	r0 = (s0 >> 1) | ((s1 & u32(1)) << 31)
	r1 = (s1 >> 1) | ((s2 & u32(1)) << 31)
	r2 = s2 >> 1
	return r2,r1,r0
}

// left logical shift 96 bit
fn lsl96(s2 u32, s1 u32, s0 u32) (u32, u32, u32) {
	mut r0 := u32(0)
	mut r1 := u32(0)
	mut r2 := u32(0)
	r2 = (s2 << 1) | ((s1 & (u32(1) << 31)) >> 31)
	r1 = (s1 << 1) | ((s0 & (u32(1) << 31)) >> 31)
	r0 = s0 << 1
	return r2,r1,r0
}

// sum on 96 bit
fn add96(s2 u32, s1 u32, s0 u32, d2 u32, d1 u32, d0 u32) (u32, u32, u32) {
	mut w  := u64(0)
	mut r0 := u32(0)
	mut r1 := u32(0)
	mut r2 := u32(0)
	w = u64(s0) + u64(d0)
	r0 = u32(w)
	w >>= 32
	w += u64(s1) + u64(d1)
	r1 = u32(w)
	w >>= 32
	w += u64(s2) + u64(d2)
	r2 = u32(w)
	return r2,r1,r0
}

// subtraction on 96 bit
fn sub96(s2 u32, s1 u32, s0 u32, d2 u32, d1 u32, d0 u32) (u32, u32, u32) {
	mut w  := u64(0)
	mut r0 := u32(0)
	mut r1 := u32(0)
	mut r2 := u32(0)
	w = u64(s0) - u64(d0)
	r0 = u32(w)
	w >>= 32
	w += u64(s1) - u64(d1)
	r1 = u32(w)
	w >>= 32
	w += u64(s2) - u64(d2)
	r2 = u32(w)
	return r2,r1,r0
}

/**********************************************************************
*
* Constants
*
**********************************************************************/
const (
	//
	// f64 constants
	//
	DIGITS = 18
	DOUBLE_PLUS_ZERO		= u64(0x0000000000000000)
	DOUBLE_MINUS_ZERO		= 0x8000000000000000
	DOUBLE_PLUS_INFINITY	= 0x7FF0000000000000
	DOUBLE_MINUS_INFINITY	= 0xFFF0000000000000

	//
	// parser state machine states
	//
	FSM_A    = 0
	FSM_B    = 1
	FSM_C    = 2
	FSM_D    = 3
	FSM_E    = 4
	FSM_F    = 5
	FSM_G    = 6
	FSM_H    = 7
	FSM_I    = 8
	FSM_STOP = 9

	//
	// Possible parser return values.
	//
	PARSER_OK     = 0  // parser finished OK
	PARSER_PZERO  = 1  // no digits or number is smaller than +-2^-1022
	PARSER_MZERO  = 2  // number is negative, module smaller
	PARSER_PINF   = 3  // number is higher than +HUGE_VAL
	PARSER_MINF   = 4  // number is lower than -HUGE_VAL

	//
	// char constants
	// Note: Modify these if working with non-ASCII encoding
	//
	DPOINT   =`.`
	PLUS     =`+`
	MINUS    =`-`
	ZERO     =`0`
	NINE     =`9`

	TEN      = u32(10)
)


/**********************************************************************
*
* Utility
*
**********************************************************************/
// NOTE: Modify these if working with non-ASCII encoding

fn is_digit(x byte) bool {
	return (x >= ZERO && x <=NINE) == true
}

fn is_space(x byte) bool {
	return ((x >= 0x89 && x <= 0x13) || x == 0x20) == true
}

fn is_exp(x byte) bool {
	return (x == `E` || x == `e`) == true
}

/*
// return a string of the input f64 in scientific notation with digit_num digits displayed
pub fn strsci(x f64, digit_num int) string{
	buf := malloc(digit_num*2+2)// TODO
	conf_str := '%0.'+digit_num.str()+'e'
	C.sprintf(charptr(buf), charptr(conf_str.str), x)
	tmpstr := tos(buf, vstrlen(buf))
	return tmpstr
}

// return a long string of the input f64, max  
pub fn strlong(x f64) string {
	buf := malloc(18+32)// TODO
	C.sprintf(charptr(buf),"%0.30lf",x)
	tmpstr := tos(buf, vstrlen(buf))
	return tmpstr
}
*/

/**********************************************************************
*
* Support struct
*
**********************************************************************/
// The structure is filled by parser, then given to converter.
pub struct PrepNumber
{
pub mut:
	negative bool = false   // 0 if positive number, 1 if negative
	exponent int  = 0       // power of 10 exponent
	mantissa u64  = u64(0)  // integer mantissa
}


/**********************************************************************
*
* String parser
* NOTE: #TOFIX need one char after the last char of the number
*
**********************************************************************/
// parser return a support struct with all the parsing information for the converter
fn parser(s string ) (int,PrepNumber) {
	mut state 	   := FSM_A
	mut digx       := 0
	mut c          := ` `          // initial value for kicking off the state machine
	mut result     := PARSER_OK
	mut expneg     := false
	mut expexp     := 0
	mut i          := 0

	mut pn := PrepNumber{}

	for state != FSM_STOP {
		
		match  state {

			// skip starting spaces
			FSM_A {
				if is_space(c)==true {
					c = s[i++]
				} else {
				 	state = FSM_B
				}
			}

			// check for the sign or point
			FSM_B {
				state = FSM_C

				if c == PLUS {
					c = s[i++]
				} else if c == MINUS {
					pn.negative = true
					c = s[i++]
				} else if  is_digit(c) {}
				else if c == DPOINT {}
				else {
					state = FSM_STOP
				}
			}

			// skip the inital zeros
			FSM_C {
				if c == ZERO { c = s[i++] }
				else if c == DPOINT {
					c = s[i++]
					state = FSM_D
				} else {
					state = FSM_E
				}
			}
			
			// reading leading zeros in the fractional part of mantissa
			FSM_D {
				if c == ZERO {
					c = s[i++]
					if pn.exponent > -2147483647 { pn.exponent-- }
				}
				else {
					state = FSM_F
				}
			}

			// reading integer part of mantissa
			FSM_E {
				if is_digit(c) {
					if digx < DIGITS {
						pn.mantissa *= 10
						pn.mantissa += u64( c - ZERO )
						digx++
					}
					else if pn.exponent < 2147483647 { pn.exponent++ }

					c = s[i++]

				}
				else if c == DPOINT {
					c = s[i++]
					state = FSM_F
				}
				else {
					state = FSM_F
				}
			}

			// reading fractional part of mantissa
			FSM_F {
				if is_digit(c) {
					if digx < DIGITS {
						pn.mantissa *= 10
						pn.mantissa += u64(c - ZERO)
						pn.exponent--
						digx++
					}

					c = s[i++]
				}
				else if is_exp(c) {
					c = s[i++]
					state = FSM_G
				}
				else {
					state = FSM_G
				}
			}

			// reading sign of exponent
			FSM_G {
				if (c == PLUS) {
					c = s[i++]
				} else if c == MINUS {
					expneg = true
					c = s[i++]
				}
				state = FSM_H
			}

			// skipping leading zeros of exponent
			FSM_H {
				if c == ZERO {
					c = s[i++]
				}
				else {
					state = FSM_I
				}
			}

			// reading exponent digits
			FSM_I {
				if is_digit(c) {
					if expexp < 214748364 {
						expexp *= 10
						expexp += int(c - ZERO)
					}

					c = s[i++]
				}
				else {
					state = FSM_STOP
				}
			}

			else {}
		}
		
		//C.printf("len: %d i: %d str: %s \n",s.len,i,s[..i])
		if i>=s.len {
			state = FSM_STOP
		}
	}

	if expneg {
		expexp = -expexp
	}
	pn.exponent += expexp

	if pn.mantissa == 0 {
		if pn.negative {
			result = PARSER_MZERO
		} else {
			result = PARSER_PZERO
		}
	}
	else if (pn.exponent > 309){
		if pn.negative {
			result = PARSER_MINF
		} else {
			result = PARSER_PINF
		}
	}
	else if pn.exponent < -328 {
		if pn.negative {
			result = PARSER_MZERO
		} else {
			result = PARSER_PZERO
		}
	}

	return result,pn
}


/**********************************************************************
*
* Converter to the bit form of the f64 number
*
**********************************************************************/
// converter return a u64 with the bit image of the f64 number
fn converter(pn mut PrepNumber) u64 {
	mut binexp := 92
	
	mut s2:=u32(0)             // 96-bit precision integer
	mut s1:=u32(0)
	mut s0:=u32(0)
	mut q2:=u32(0)             // 96-bit precision integer
	mut q1:=u32(0)
	mut q0:=u32(0)
	mut r2:=u32(0)             // 96-bit precision integer
	mut r1:=u32(0)
	mut r0:=u32(0)
	
	mask28 := u32(0xF << 28)

	mut result := u64(0)

	// working on 3 u32 to have 96 bit precision
	s0 = u32(pn.mantissa & u64(0x00000000FFFFFFFF))
	s1 = u32(pn.mantissa >> 32)
	s2 = u32(0)

	// so we take the decimal exponent off
	for pn.exponent > 0 {
		q2, q1, q0 = lsl96(s2, s1, s0)   // q = s * 2
		r2, r1, r0 = lsl96(q2, q1, q0)   // r = s * 4 <=> q * 2
		s2, s1, s0 = lsl96(r2, r1, r0)   // s = s * 8 <=> r * 2
		s2, s1, s0 = add96(s2, s1, s0, q2, q1, q0)   // s = (s * 8) + (s * 2) <=> s*10

		pn.exponent--

		for (s2 & mask28) != 0 {
			q2, q1, q0 = lsr96(s2, s1, s0)
			binexp++
			s2 = q2
			s1 = q1
			s0 = q0
		}

	}

	for pn.exponent < 0 {
		for !((s2 & (u32(1) << 31)) !=0) {
			q2, q1, q0 = lsl96(s2, s1, s0)
			binexp--
			s2 = q2
			s1 = q1
			s0 = q0

		}

		q2 = s2 / TEN
		r1 = s2 % TEN
		r2 = (s1 >> 8) | (r1 << 24)
		q1 = r2 / TEN
		r1 = r2 % TEN
		r2 = ((s1 & u32(0xFF)) << 16) | (s0 >> 16) | (r1 << 24)
		r0 = r2 / TEN
		r1 = r2 % TEN
		q1 = (q1 << 8) | ((r0 & u32(0x00FF0000)) >> 16)
		q0 = r0 << 16
		r2 = (s0 & u32(0xFFFF)) | (r1 << 16)
		q0 |= r2 / TEN
		s2 = q2
		s1 = q1
		s0 = q0

		pn.exponent++
		
	}

	//C.printf("mantissa before normalization: %08x%08x%08x binexp: %d \n", s2,s1,s0,binexp)

	// normalization, the 28 bit in s2 must the leftest one in the variable
	if (s2 != 0 || s1 != 0|| s0 != 0) {
		for ((s2 & mask28) == 0) {
			q2, q1, q0 = lsl96(s2, s1, s0)
			binexp--
			s2 = q2
			s1 = q1
			s0 = q0
		}
	}

	// rounding if needed
	/*
	* "round half to even" algorithm
	* Example for f32, just a reminder
	*
	* If bit 54 is 0, round down
	* If bit 54 is 1
	*	If any bit beyond bit 54 is 1, round up
	*	If all bits beyond bit 54 are 0 (meaning the number is halfway between two floating-point numbers)
	*		If bit 53 is 0, round down
	*		If bit 53 is 1, round up
	*/

	/* test case 1 complete
	s2=0x1FFFFFFF
	s1=0xFFFFFF80
	s0=0x0
	*/

	/* test case 1 check_round_bit
	s2=0x18888888
	s1=0x88888880
	s0=0x0
	*/

	/* test case  check_round_bit + normalization
	s2=0x18888888
	s1=0x88888F80
	s0=0x0
	*/

	//C.printf("mantissa before rounding: %08x%08x%08x binexp: %d \n", s2,s1,s0,binexp)
	
	// s1 => 0xFFFFFFxx only F are rapresented
	nbit := 7
	check_round_bit := u32(1) << u32(nbit)
	check_round_mask := u32(0xFFFFFFFF) << u32(nbit)

	if (s1 & check_round_bit) != 0 {
		//C.printf("need round!! cehck mask: %08x\n", s1 & ~check_round_mask )
		if (s1 & ~check_round_mask) != 0 {
			//C.printf("Add 1!\n")
			s2,s1,s0 = add96(s2,s1,s0, 0,check_round_bit,0)
		} else {
			//C.printf("All 0!\n")
			if (s1 & (check_round_bit<<u32(1) )) != 0 {
				//C.printf("Add 1 form -1 bit control!\n")
				s2,s1,s0 = add96(s2,s1,s0, 0,check_round_bit,0)
			}
		}
		s1 = s1 & check_round_mask
		s0 = u32(0)
	}

	// recheck normalization
	if (s2 & (mask28<<u32(1)) != 0 ) {
		//C.printf("Renormalize!!")
		q2, q1, q0 = lsr96(s2, s1, s0)
		binexp--
		s2 = q2
		s1 = q1
		s0 = q0
	}

	//tmp := ( u64(s2 & ~mask28) << 24) | ((u64(s1) + u64(128)) >> 8)
	//C.printf("mantissa after rounding : %08x%08x%08x binexp: %d \n", s2,s1,s0,binexp)
	//C.printf("Tmp result: %016x\n",tmp)
	
	// end rounding
	
	// offset the binary exponent IEEE 754
	binexp += 1023

	if (binexp > 2046) {
		if pn.negative {
			result = DOUBLE_MINUS_INFINITY
		} else {
			result = DOUBLE_PLUS_INFINITY
		}
	}
	else if binexp < 1 {
		if pn.negative {
			result = DOUBLE_MINUS_ZERO
		}
	}
	else if s2 != 0 {
		mut q := u64(0)
		binexs2 := u64(binexp) << 52

		q = ( u64(s2 & ~mask28) << 24) | ((u64(s1) + u64(128)) >> 8) | binexs2
		if pn.negative {
			q |= (u64(1) << 63)
		}
		result = q
	}

	return result
}

/**********************************************************************
*
* Public functions
*
**********************************************************************/
// atof64 return a f64 from a string doing a parsing operation
pub fn atof64(s string) f64 {
	mut pn := PrepNumber{}
	mut res_parsing := 0
	
	mut result := f64(0)
	result=f64(0.0)
	mut res_ptr := *u64(&result)
	
	res_parsing, pn = parser(s+' ') // TODO: need an extra char for now
	//println(pn)
	
	match res_parsing {
		PARSER_OK {
			*res_ptr = converter( mut pn)
		}
		PARSER_PZERO {
			*res_ptr = DOUBLE_PLUS_ZERO
		}
		PARSER_MZERO {
			*res_ptr = DOUBLE_MINUS_ZERO
		}
		PARSER_PINF {
			*res_ptr = DOUBLE_PLUS_INFINITY
		}
		PARSER_MINF {
			*res_ptr = DOUBLE_MINUS_INFINITY
		}
		else {}
	}
	return result
}