v/vlib/strconv/ftoa/utilities.v

/**********************************************************************
*
* f32/f64 to string utilities 
*
* Copyright (c) 2019-2020 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 the f32/f64 to string utilities functions
*
* These functions are based on the work of:
* Publication:PLDI 2018: Proceedings of the 39th ACM SIGPLAN 
* Conference on Programming Language Design and ImplementationJune 2018 
* Pages 270–282 https://doi.org/10.1145/3192366.3192369
*
* inspired by the Go version here: 
* https://github.com/cespare/ryu/tree/ba56a33f39e3bbbfa409095d0f9ae168a595feea
*
**********************************************************************/
module ftoa
import math
import math.bits

/******************************************************************************
*
* General Utilities
*
******************************************************************************/
fn assert1(t bool, msg string) {
	if !t {
		panic(msg)
	}
}

[inline]
fn bool_to_int(b bool) int {
	if b {
		return 1
	}
	return 0
}

[inline]
fn bool_to_u32(b bool) u32 {
	if b {
		return u32(1)
	}
	return u32(0)
}

[inline]
fn bool_to_u64(b bool) u64 {
	if b {
		return u64(1)
	}
	return u64(0)
}

fn get_string_special(neg bool, expZero bool, mantZero bool) string {
	if !mantZero {
		return "nan"
	}
	if !expZero {
		if neg {
			return "-inf"
		} else {
			return "+inf"
		}
	}
	if neg {
		return "-0e+00"
	}
	return "0e+00"
}

/******************************************************************************
*
* 32 bit functions
*
******************************************************************************/
fn decimal_len_32(u u32) int {
	// Function precondition: u is not a 10-digit number.
	// (9 digits are sufficient for round-tripping.)
	// This benchmarked faster than the log2 approach used for u64.
	assert1(u < 1000000000, "too big")
	
	if u >= 100000000     {	return 9 }
	else if u >= 10000000 {	return 8 }
	else if u >= 1000000  {	return 7 }
	else if u >= 100000   {	return 6 }
	else if u >= 10000    {	return 5 }
	else if u >= 1000     { return 4 }
	else if u >= 100      {	return 3 }
	else if u >= 10       {	return 2 }
	return 1
}

fn mul_shift_32(m u32, mul u64, ishift int) u32 {
	assert ishift > 32

	hi, lo := bits.mul_64(u64(m), mul)
	shifted_sum := (lo >> u64(ishift)) + (hi << u64(64-ishift))
	assert1(shifted_sum <= math.max_u32, "shiftedSum <= math.max_u32")
	return u32(shifted_sum)
}

fn mul_pow5_invdiv_pow2(m u32, q u32, j int) u32 {
	return mul_shift_32(m, pow5_inv_split_32[q], j)
}

fn mul_pow5_div_pow2(m u32, i u32, j int) u32 {
	return mul_shift_32(m, pow5_split_32[i], j)
}

fn pow5_factor_32(i_v u32) u32 {
	mut v := i_v
	for n := u32(0); ; n++ {
		q := v/5 
		r := v%5
		if r != 0 {
			return n
		}
		v = q
	}
	return v
}

// multiple_of_power_of_five_32 reports whether v is divisible by 5^p.
fn multiple_of_power_of_five_32(v u32, p u32) bool {
	return pow5_factor_32(v) >= p
}

// multiple_of_power_of_two_32 reports whether v is divisible by 2^p.
fn multiple_of_power_of_two_32(v u32, p u32) bool {
	return bits.trailing_zeros_32(v) >= p
}

// log10_pow2 returns floor(log_10(2^e)).
fn log10_pow2(e int) u32 {
	// The first value this approximation fails for is 2^1651
	// which is just greater than 10^297.
	assert1(e >= 0, "e >= 0")
	assert1(e <= 1650, "e <= 1650")
	return (u32(e) * 78913) >> 18
}

// log10_pow5 returns floor(log_10(5^e)).
fn log10_pow5(e int) u32 {
	// The first value this approximation fails for is 5^2621
	// which is just greater than 10^1832.
	assert1(e >= 0, "e >= 0")
	assert1(e <= 2620, "e <= 2620")
	return (u32(e) * 732923) >> 20
}

// pow5_bits returns ceil(log_2(5^e)), or else 1 if e==0.
fn pow5_bits(e int) int {
	// This approximation works up to the point that the multiplication
	// overflows at e = 3529. If the multiplication were done in 64 bits,
	// it would fail at 5^4004 which is just greater than 2^9297.
	assert1(e >= 0, "e >= 0")
	assert1(e <= 3528, "e <= 3528")
	return int( ((u32(e)*1217359)>>19) + 1)
}

/******************************************************************************
*
* 64 bit functions
*
******************************************************************************/
fn decimal_len_64(u u64) int {
	// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10
	log2 := 64 - bits.leading_zeros_64(u) - 1
	t := (log2 + 1) * 1233 >> 12
	return t - bool_to_int(u < powers_of_10[t]) + 1
}

fn shift_right_128(v Uint128, shift int) u64 {
	// The shift value is always modulo 64.
	// In the current implementation of the 64-bit version
	// of Ryu, the shift value is always < 64.
	// (It is in the range [2, 59].)
	// Check this here in case a future change requires larger shift
	// values. In this case this function needs to be adjusted.
	assert1(shift < 64, "shift < 64")
	return (v.hi << u64(64 - shift)) | (v.lo >> u32(shift))
}

fn mul_shift_64(m u64, mul Uint128, shift int) u64 {
	hihi, hilo := bits.mul_64(m, mul.hi)
	lohi, _    := bits.mul_64(m, mul.lo)
	mut sum := Uint128{hi: hihi, lo: lohi + hilo}
	if sum.lo < lohi {
		sum.hi++ // overflow
	}
	return shift_right_128(sum, shift-64)
}

fn pow5_factor_64(v_i u64) u32 {
	mut v := v_i
	for n := u32(0); ; n++ {
		q := v/5
		r := v%5
		if r != 0 {
			return n
		}
		v = q
	}
	return u32(0)
}

fn multiple_of_power_of_five_64(v u64, p u32) bool {
	return pow5_factor_64(v) >= p
}

fn multiple_of_power_of_two_64(v u64, p u32) bool {
	return u32(bits.trailing_zeros_64(v)) >= p
}

/******************************************************************************
*
* f64 to string with string format
*
******************************************************************************/

// f32_to_str_l return a string with the f32 converted in a strign in decimal notation
pub fn f32_to_str_l(f f64) string {
	return f64_to_str_l(f32(f))
}

// f64_to_str_l return a string with the f64 converted in a strign in decimal notation
pub fn f64_to_str_l(f f64) string {
	s := f64_to_str(f,18)

	// check for +inf -inf Nan
	if s.len > 2 && (s[0] == `N` || s[1] == `i`) {
		return s
	} 

	m_sgn_flag := false
	mut sgn        := 1
	mut b          := [18+8]byte
	mut d_pos      := 1
	mut i          := 0
	mut i1         := 0
	mut exp        := 0
	mut exp_sgn    := 1

	// get sign and deciaml parts
	for c in s {
		if c == `-` {
			sgn = -1
			i++
		} else if c == `+` {
			sgn = 1
			i++
		}
		else if c >= `0` && c <= `9` {
			b[i1++] = c
			i++
		} else if c == `.` {
			if sgn > 0 {
				d_pos = i
			} else {
				d_pos = i-1
			}
			i++
		} else if c == `e` {
			i++
			break
		} else {
			return "Float conversion error!!"
		}
	}
	b[i1] = 0

	// get exponent
	if s[i] == `-` {
		exp_sgn = -1
		i++
	} else if s[i] == `+` {
		exp_sgn = 1
		i++
	}
	for c in s[i..] {
		exp = exp * 10 + int(c-`0`)
	}

	// allocate exp+32 chars for the return string
	mut res := [`0`].repeat(exp+32) // TODO: Slow!! is there other possibilities to allocate this?
	mut r_i := 0  // result string buffer index
	
	//println("s:${sgn} b:${b[0]} es:${exp_sgn} exp:${exp}")

	if sgn == 1 {
		if m_sgn_flag {
			res[r_i++] = `+`
		}
	} else {
		res[r_i++] = `-`
	}

	i = 0
	if exp_sgn >= 0 {
		for b[i] != 0 {
			res[r_i++] = b[i]
			i++
			if i >= d_pos && exp >= 0 {
				if exp == 0 {
					res[r_i++] = `.`
				}
				exp--
			}
		}
		for exp >= 0 {
			res[r_i++] = `0`
			exp--
		}
	} else {
		mut dot_p := true
		for exp > 0 {
			res[r_i++] = `0`
			exp--
			if dot_p  {
				res[r_i++] = `.`
				dot_p = false
			}
		}
		for b[i] != 0 {
			res[r_i++] = b[i]
			i++	
		}
	}
	res[r_i] = 0
	return tos(&res[0],r_i)
}