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v/vlib/strconv/ftoa/utilities.v

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ftoa in V (#3831)
2020-02-25 11:12:37 +01:00
/**********************************************************************
*
* 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 := ftoa.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 := [32]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)
}