v/vlib/strconv/atof.v

module strconv

/*
atof util

Copyright (c) 2019-2021 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

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     = u64(0x8000000000000000)
	double_plus_infinity  = u64(0x7FF0000000000000)
	double_minus_infinity = u64(0xFFF0000000000000)
	//
	// 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
	//
	c_dpoint              = `.`
	c_plus                = `+`
	c_minus               = `-`
	c_zero                = `0`
	c_nine                = `9`
	c_ten                 = u32(10)
)

/*
Utility
*/

// NOTE: Modify these if working with non-ASCII encoding
fn is_digit(x byte) bool {
	return (x >= strconv.c_zero && x <= strconv.c_nine) == true
}

fn is_space(x byte) bool {
	return (x == `\t` || x == `\n` || x == `\v` || x == `\f` || x == `\r` || x == ` `)
}

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

/*
Support struct
*/

/*
String parser
NOTE: #TOFIX need one char after the last char of the number
*/

fn parser(s string) (int, PrepNumber) {
	mut digx := 0
	mut result := strconv.parser_ok
	mut expneg := false
	mut expexp := 0
	mut i := 0
	mut pn := PrepNumber{}

	// skip spaces
	for i < s.len && s[i].is_space() {
		i++
	}

	// check negatives
	if s[i] == `-` {
		pn.negative = true
		i++
	}

	// positive sign ignore it
	if s[i] == `+` {
		i++
	}

	// read mantissa
	for i < s.len && s[i].is_digit() {
		// println("$i => ${s[i]}")
		if digx < strconv.digits {
			pn.mantissa *= 10
			pn.mantissa += u64(s[i] - strconv.c_zero)
			digx++
		} else if pn.exponent < 2147483647 {
			pn.exponent++
		}
		i++
	}

	// read mantissa decimals
	if (i < s.len) && (s[i] == `.`) {
		i++
		for i < s.len && s[i].is_digit() {
			if digx < strconv.digits {
				pn.mantissa *= 10
				pn.mantissa += u64(s[i] - strconv.c_zero)
				pn.exponent--
				digx++
			}
			i++
		}
	}

	// read exponent
	if (i < s.len) && ((s[i] == `e`) || (s[i] == `E`)) {
		i++
		if i < s.len {
			// esponent sign
			if s[i] == strconv.c_plus {
				i++
			} else if s[i] == strconv.c_minus {
				expneg = true
				i++
			}

			for i < s.len && s[i].is_digit() {
				if expexp < 214748364 {
					expexp *= 10
					expexp += int(s[i] - strconv.c_zero)
				}
				i++
			}
		}
	}

	if expneg {
		expexp = -expexp
	}
	pn.exponent += expexp
	if pn.mantissa == 0 {
		if pn.negative {
			result = strconv.parser_mzero
		} else {
			result = strconv.parser_pzero
		}
	} else if pn.exponent > 309 {
		if pn.negative {
			result = strconv.parser_minf
		} else {
			result = strconv.parser_pinf
		}
	} else if pn.exponent < -328 {
		if pn.negative {
			result = strconv.parser_mzero
		} else {
			result = strconv.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(mut pn 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(u64(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 / strconv.c_ten
		r1 = s2 % strconv.c_ten
		r2 = (s1 >> 8) | (r1 << 24)
		q1 = r2 / strconv.c_ten
		r1 = r2 % strconv.c_ten
		r2 = ((s1 & u32(0xFF)) << 16) | (s0 >> 16) | (r1 << 24)
		r0 = r2 / strconv.c_ten
		r1 = r2 % strconv.c_ten
		q1 = (q1 << 8) | ((r0 & u32(0x00FF0000)) >> 16)
		q0 = r0 << 16
		r2 = (s0 & u32(0xFFFF)) | (r1 << 16)
		q0 |= r2 / strconv.c_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 = strconv.double_minus_infinity
		} else {
			result = strconv.double_plus_infinity
		}
	} else if binexp < 1 {
		if pn.negative {
			result = strconv.double_minus_zero
		} else {
			result = strconv.double_plus_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 res := Float64u{}

	res_parsing, pn = parser(s)
	match res_parsing {
		strconv.parser_ok {
			res.u = converter(mut pn)
		}
		strconv.parser_pzero {
			res.u = strconv.double_plus_zero
		}
		strconv.parser_mzero {
			res.u = strconv.double_minus_zero
		}
		strconv.parser_pinf {
			res.u = strconv.double_plus_infinity
		}
		strconv.parser_minf {
			res.u = strconv.double_minus_infinity
		}
		else {}
	}
	return unsafe { res.f }
}