mirror of
https://github.com/vlang/v.git
synced 2023-08-10 21:13:21 +03:00
384 lines
8.8 KiB
V
384 lines
8.8 KiB
V
/*
|
||
|
||
f32 to string
|
||
|
||
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 to string 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
|
||
|
||
// dec32 is a floating decimal type representing m * 10^e.
|
||
struct Dec32 {
|
||
mut:
|
||
m u32 = 0
|
||
e int = 0
|
||
}
|
||
|
||
// support union for convert f32 to u32
|
||
union Uf32 {
|
||
mut:
|
||
f f32 = 0
|
||
u u32
|
||
}
|
||
|
||
// pow of ten table used by n_digit reduction
|
||
const(
|
||
ten_pow_table_32 = [
|
||
u32(1),
|
||
u32(10),
|
||
u32(100),
|
||
u32(1000),
|
||
u32(10000),
|
||
u32(100000),
|
||
u32(1000000),
|
||
u32(10000000),
|
||
u32(100000000),
|
||
u32(1000000000),
|
||
u32(10000000000),
|
||
u32(100000000000),
|
||
]
|
||
)
|
||
|
||
/*
|
||
|
||
Conversion Functions
|
||
|
||
*/
|
||
const(
|
||
mantbits32 = u32(23)
|
||
expbits32 = u32(8)
|
||
bias32 = 127 // f32 exponent bias
|
||
maxexp32 = 255
|
||
)
|
||
|
||
// max 46 char
|
||
// -3.40282346638528859811704183484516925440e+38
|
||
fn (d Dec32) get_string_32(neg bool, i_n_digit int, i_pad_digit int) string {
|
||
n_digit := i_n_digit + 1
|
||
pad_digit := i_pad_digit + 1
|
||
mut out := d.m
|
||
mut out_len := decimal_len_32(out)
|
||
out_len_original := out_len
|
||
|
||
mut fw_zeros := 0
|
||
if pad_digit > out_len {
|
||
fw_zeros = pad_digit -out_len
|
||
}
|
||
|
||
mut buf := [byte(0)].repeat(out_len + 5 + 1 +1) // sign + mant_len + . + e + e_sign + exp_len(2) + \0
|
||
mut i := 0
|
||
|
||
if neg {
|
||
buf[i]=`-`
|
||
i++
|
||
}
|
||
|
||
mut disp := 0
|
||
if out_len <= 1 {
|
||
disp = 1
|
||
}
|
||
|
||
if n_digit < out_len {
|
||
//println("orig: ${out_len_original}")
|
||
out += ten_pow_table_32[out_len - n_digit - 1] * 5 // round to up
|
||
out /= ten_pow_table_32[out_len - n_digit]
|
||
out_len = n_digit
|
||
}
|
||
|
||
y := i + out_len
|
||
mut x := 0
|
||
for x < (out_len-disp-1) {
|
||
buf[y - x] = `0` + byte(out%10)
|
||
out /= 10
|
||
i++
|
||
x++
|
||
}
|
||
|
||
if out_len >= 1 {
|
||
buf[y - x] = `.`
|
||
x++
|
||
i++
|
||
}
|
||
|
||
if y-x >= 0 {
|
||
buf[y - x] = `0` + byte(out%10)
|
||
i++
|
||
}
|
||
|
||
for fw_zeros > 0 {
|
||
buf[i++] = `0`
|
||
fw_zeros--
|
||
}
|
||
|
||
/*
|
||
x=0
|
||
for x<buf.len {
|
||
C.printf("d:%c\n",buf[x])
|
||
x++
|
||
}
|
||
C.printf("\n")
|
||
*/
|
||
|
||
buf[i]=`e`
|
||
i++
|
||
|
||
mut exp := d.e + out_len_original - 1
|
||
if exp < 0 {
|
||
buf[i]=`-`
|
||
i++
|
||
exp = -exp
|
||
} else {
|
||
buf[i]=`+`
|
||
i++
|
||
}
|
||
|
||
// Always print two digits to match strconv's formatting.
|
||
d1 := exp % 10
|
||
d0 := exp / 10
|
||
buf[i]=`0` + byte(d0)
|
||
i++
|
||
buf[i]=`0` + byte(d1)
|
||
i++
|
||
buf[i]=0
|
||
|
||
/*
|
||
x=0
|
||
for x<buf.len {
|
||
C.printf("d:%c\n",buf[x])
|
||
x++
|
||
}
|
||
*/
|
||
return tos(byteptr(&buf[0]), i)
|
||
}
|
||
|
||
fn f32_to_decimal_exact_int(i_mant u32, exp u32) (Dec32,bool) {
|
||
mut d := Dec32{}
|
||
e := exp - bias32
|
||
if e > mantbits32 {
|
||
return d, false
|
||
}
|
||
shift := mantbits32 - e
|
||
mant := i_mant | 0x0080_0000 // implicit 1
|
||
//mant := i_mant | (1 << mantbits32) // implicit 1
|
||
d.m = mant >> shift
|
||
if (d.m << shift) != mant {
|
||
return d, false
|
||
}
|
||
for (d.m % 10) == 0 {
|
||
d.m /= 10
|
||
d.e++
|
||
}
|
||
return d, true
|
||
}
|
||
|
||
pub fn f32_to_decimal(mant u32, exp u32) Dec32 {
|
||
mut e2 := 0
|
||
mut m2 := u32(0)
|
||
if exp == 0 {
|
||
// We subtract 2 so that the bounds computation has
|
||
// 2 additional bits.
|
||
e2 = 1 - bias32 - int(mantbits32) - 2
|
||
m2 = mant
|
||
} else {
|
||
e2 = int(exp) - bias32 - int(mantbits32) - 2
|
||
m2 = (u32(1) << mantbits32) | mant
|
||
}
|
||
even := (m2 & 1) == 0
|
||
accept_bounds := even
|
||
|
||
// Step 2: Determine the interval of valid decimal representations.
|
||
mv := u32(4 * m2)
|
||
mp := u32(4 * m2 + 2)
|
||
mm_shift := bool_to_u32(mant != 0 || exp <= 1)
|
||
mm := u32(4 * m2 - 1 - mm_shift)
|
||
|
||
mut vr := u32(0)
|
||
mut vp := u32(0)
|
||
mut vm := u32(0)
|
||
mut e10 := 0
|
||
mut vm_is_trailing_zeros := false
|
||
mut vr_is_trailing_zeros := false
|
||
mut last_removed_digit := byte(0)
|
||
|
||
if e2 >= 0 {
|
||
q := log10_pow2(e2)
|
||
e10 = int(q)
|
||
k := pow5_inv_num_bits_32 + pow5_bits(int(q)) - 1
|
||
i := -e2 + int(q) + k
|
||
|
||
vr = mul_pow5_invdiv_pow2(mv, q, i)
|
||
vp = mul_pow5_invdiv_pow2(mp, q, i)
|
||
vm = mul_pow5_invdiv_pow2(mm, q, i)
|
||
if q != 0 && (vp-1)/10 <= vm/10 {
|
||
// We need to know one removed digit even if we are not
|
||
// going to loop below. We could use q = X - 1 above,
|
||
// except that would require 33 bits for the result, and
|
||
// we've found that 32-bit arithmetic is faster even on
|
||
// 64-bit machines.
|
||
l := pow5_inv_num_bits_32 + pow5_bits(int(q - 1)) - 1
|
||
last_removed_digit = byte(mul_pow5_invdiv_pow2(mv, q - 1, -e2 + int(q - 1) + l) % 10)
|
||
}
|
||
if q <= 9 {
|
||
// The largest power of 5 that fits in 24 bits is 5^10,
|
||
// but q <= 9 seems to be safe as well. Only one of mp,
|
||
// mv, and mm can be a multiple of 5, if any.
|
||
if mv%5 == 0 {
|
||
vr_is_trailing_zeros = multiple_of_power_of_five_32(mv, q)
|
||
} else if accept_bounds {
|
||
vm_is_trailing_zeros = multiple_of_power_of_five_32(mm, q)
|
||
} else if multiple_of_power_of_five_32(mp, q) {
|
||
vp--
|
||
}
|
||
}
|
||
} else {
|
||
q := log10_pow5(-e2)
|
||
e10 = int(q) + e2
|
||
i := -e2 - int(q)
|
||
k := pow5_bits(i) - pow5_num_bits_32
|
||
mut j := int(q) - k
|
||
vr = mul_pow5_div_pow2(mv, u32(i), j)
|
||
vp = mul_pow5_div_pow2(mp, u32(i), j)
|
||
vm = mul_pow5_div_pow2(mm, u32(i), j)
|
||
if q != 0 && ((vp-1)/10) <= vm/10 {
|
||
j = int(q) - 1 - (pow5_bits(i + 1) - pow5_num_bits_32)
|
||
last_removed_digit = byte(mul_pow5_div_pow2(mv, u32(i + 1), j) % 10)
|
||
}
|
||
if q <= 1 {
|
||
// {vr,vp,vm} is trailing zeros if {mv,mp,mm} has at
|
||
// least q trailing 0 bits. mv = 4 * m2, so it always
|
||
// has at least two trailing 0 bits.
|
||
vr_is_trailing_zeros = true
|
||
if accept_bounds {
|
||
// mm = mv - 1 - mm_shift, so it has 1 trailing 0 bit
|
||
// if mm_shift == 1.
|
||
vm_is_trailing_zeros = mm_shift == 1
|
||
} else {
|
||
// mp = mv + 2, so it always has at least one
|
||
// trailing 0 bit.
|
||
vp--
|
||
}
|
||
} else if q < 31 {
|
||
vr_is_trailing_zeros = multiple_of_power_of_two_32(mv, q - 1)
|
||
}
|
||
}
|
||
|
||
// Step 4: Find the shortest decimal representation
|
||
// in the interval of valid representations.
|
||
mut removed := 0
|
||
mut out := u32(0)
|
||
if vm_is_trailing_zeros || vr_is_trailing_zeros {
|
||
// General case, which happens rarely (~4.0%).
|
||
for vp/10 > vm/10 {
|
||
vm_is_trailing_zeros = vm_is_trailing_zeros && (vm % 10) == 0
|
||
vr_is_trailing_zeros = vr_is_trailing_zeros && (last_removed_digit == 0)
|
||
last_removed_digit = byte(vr % 10)
|
||
vr /= 10
|
||
vp /= 10
|
||
vm /= 10
|
||
removed++
|
||
}
|
||
if vm_is_trailing_zeros {
|
||
for vm%10 == 0 {
|
||
vr_is_trailing_zeros = vr_is_trailing_zeros && (last_removed_digit == 0)
|
||
last_removed_digit = byte(vr % 10)
|
||
vr /= 10
|
||
vp /= 10
|
||
vm /= 10
|
||
removed++
|
||
}
|
||
}
|
||
if vr_is_trailing_zeros && (last_removed_digit == 5) && (vr % 2) == 0 {
|
||
// Round even if the exact number is .....50..0.
|
||
last_removed_digit = 4
|
||
}
|
||
out = vr
|
||
// We need to take vr + 1 if vr is outside bounds
|
||
// or we need to round up.
|
||
if (vr == vm && (!accept_bounds || !vm_is_trailing_zeros)) || last_removed_digit >= 5 {
|
||
out++
|
||
}
|
||
} else {
|
||
// Specialized for the common case (~96.0%). Percentages below
|
||
// are relative to this. Loop iterations below (approximately):
|
||
// 0: 13.6%, 1: 70.7%, 2: 14.1%, 3: 1.39%, 4: 0.14%, 5+: 0.01%
|
||
for vp/10 > vm/10 {
|
||
last_removed_digit = byte(vr % 10)
|
||
vr /= 10
|
||
vp /= 10
|
||
vm /= 10
|
||
removed++
|
||
}
|
||
// We need to take vr + 1 if vr is outside bounds
|
||
// or we need to round up.
|
||
out = vr + bool_to_u32(vr == vm || last_removed_digit >= 5)
|
||
}
|
||
|
||
return Dec32{m: out e: e10 + removed}
|
||
}
|
||
|
||
// f32_to_str return a string in scientific notation with max n_digit after the dot
|
||
pub fn f32_to_str(f f32, n_digit int) string {
|
||
mut u1 := Uf32{}
|
||
u1.f = f
|
||
u := u1.u
|
||
|
||
neg := (u>>(mantbits32+expbits32)) != 0
|
||
mant := u & ((u32(1)<<mantbits32) - u32(1))
|
||
exp := (u >> mantbits32) & ((u32(1)<<expbits32) - u32(1))
|
||
|
||
//println("${neg} ${mant} e ${exp-bias32}")
|
||
|
||
// Exit early for easy cases.
|
||
if (exp == maxexp32) || (exp == 0 && mant == 0) {
|
||
return get_string_special(neg, exp == 0, mant == 0)
|
||
}
|
||
|
||
mut d, ok := f32_to_decimal_exact_int(mant, exp)
|
||
if !ok {
|
||
//println("with exp form")
|
||
d = f32_to_decimal(mant, exp)
|
||
}
|
||
|
||
//println("${d.m} ${d.e}")
|
||
return d.get_string_32(neg, n_digit,0)
|
||
}
|
||
|
||
// f32_to_str return a string in scientific notation with max n_digit after the dot
|
||
pub fn f32_to_str_pad(f f32, n_digit int) string {
|
||
mut u1 := Uf32{}
|
||
u1.f = f
|
||
u := u1.u
|
||
|
||
neg := (u>>(mantbits32+expbits32)) != 0
|
||
mant := u & ((u32(1)<<mantbits32) - u32(1))
|
||
exp := (u >> mantbits32) & ((u32(1)<<expbits32) - u32(1))
|
||
|
||
//println("${neg} ${mant} e ${exp-bias32}")
|
||
|
||
// Exit early for easy cases.
|
||
if (exp == maxexp32) || (exp == 0 && mant == 0) {
|
||
return get_string_special(neg, exp == 0, mant == 0)
|
||
}
|
||
|
||
mut d, ok := f32_to_decimal_exact_int(mant, exp)
|
||
if !ok {
|
||
//println("with exp form")
|
||
d = f32_to_decimal(mant, exp)
|
||
}
|
||
|
||
//println("${d.m} ${d.e}")
|
||
return d.get_string_32(neg, n_digit, n_digit)
|
||
}
|