archive-gh-me/jerryscript
1
0
Fork 0
mirror of https://github.com/jerryscript-project/jerryscript.git synced 2025-12-15 16:29:21 +00:00
Code Issues Projects Releases Wiki Activity

Clean up radix conversion in Number toString method (#2002)

Browse Source 
The radix conversion code path was very messy which made it hard to understand
what was happening inside of it. The code got cleaned up, and a lot of comments
were added that explain what is happening and why.

JerryScript-DCO-1.0-Signed-off-by: Dániel Bátyai dbatyai@inf.u-szeged.hu
This commit is contained in:
Dániel Bátyai 2017-09-06 10:56:29 +02:00 committed by GitHub
parent 74045f2964
commit 01dd2f0b2a
2 changed files with 124 additions and 69 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

191
jerry-core/ecma/builtin-objects/ecma-builtin-number-prototype.c
View File

@ -266,90 +266,132 @@ ecma_builtin_number_prototype_object_to_string (ecma_value_t this_arg, /**< this
}
else
{
bool is_negative = false;
int buff_size = 0;
bool is_number_negative = false;
if (ecma_number_is_negative (this_arg_number))
{
/* ecma_number_to_decimal can't handle negative numbers, so we get rid of the sign. */
this_arg_number = -this_arg_number;
is_negative = true;
is_number_negative = true;
/* Add space for the sign in the result. */
buff_size += 1;
}
/* Decompose the number. */
lit_utf8_byte_t digits[ECMA_MAX_CHARS_IN_STRINGIFIED_NUMBER];
int32_t exponent;
lit_utf8_size_t num_digits = ecma_number_to_decimal (this_arg_number, digits, &exponent);
lit_utf8_size_t digit_count = ecma_number_to_decimal (this_arg_number, digits, &exponent);
exponent = exponent - (int32_t) num_digits;
/*
* The 'exponent' given by 'ecma_number_to_decimal' specifies where the decimal point is located
* compared to the first digit in 'digits'.
* For example: 120 -> '12', exp: 3 and 0.012 -> '12', exp: -1
* We convert it to be location of the decimal point compared to the last digit of 'digits':
* 120 -> 12 * 10^1 and 0.012 -> 12 * 10^-3
*/
exponent = exponent - (int32_t) digit_count;
/* Calculate the scale of the number in the specified radix. */
int scale = (int) -floor ((log (10) / log (radix)) * exponent);
bool is_scale_negative = false;
if (scale < 0)
{
is_scale_negative = true;
scale = -scale;
}
int buff_size = 1;
if (is_scale_negative || scale == 0)
/* 'magnitude' will be the magnitude of the number in the specific radix. */
int magnitude;
int required_digits;
if (exponent >= 0)
{
/*
* If the exponent is non-negative that means we won't have a fractional part, and can calculate
* exactly how many digits we will have. This could be done via a mathematic formula, but in rare
* cases that can cause incorrect results due to precision issues, so we use a loop instead.
*/
magnitude = 0;
double counter = this_arg_number;
while (counter >= radix)
{
counter /= radix;
buff_size++;
magnitude++;
}
/*
* The magnitude will only tell us how many digits we have after the first one, so we add one extra.
* In this case we won't be needing a radix point, so we don't need to worry about space for it.
*/
required_digits = magnitude + 1;
}
else
{
buff_size = scale + ECMA_NUMBER_FRACTION_WIDTH + 2;
/*
* We can't know exactly how many digits we will need, since the number may be non-terminating in the
* new radix, so we will have to estimate it. We do this by first calculating how many zeros we will
* need in the specific radix before we hit a significant digit. This is calculated from the decimal
* exponent, which we negate so that we get a positive number in the end.
*/
magnitude = (int) floor ((log (10) / log (radix)) * -exponent);
/*
* We also need to add space for significant digits. The worst case is radix == 2, since this will
* require the most digits. In this case, the upper limit to the number of significant digits we can have is
* ECMA_NUMBER_FRACTION_WIDTH + 1. This should be sufficient for any number.
*/
required_digits = magnitude + ECMA_NUMBER_FRACTION_WIDTH + 1;
/*
* We add an exta slot for the radix point. It is also likely that we will need extra space for a
* leading zero before the radix point. It's better to add space for that here as well, even if we may not
* need it, since later we won't be able to do so.
*/
buff_size += 2;
}
if (is_negative)
/*
* Here we normalize the number so that it is as close to 0 as possible, which will prevent us from losing
* precision in case of extreme numbers when we later split the number into integer and fractional parts.
* This has to be done in the specific radix, otherwise it messes up the result, so we use magnitude instead.
*/
if (exponent > 0)
{
buff_size++;
}
/* Normalize the number, so that it is as close to 0 exponent as possible. */
if (is_scale_negative)
{
for (int i = 0; i < scale; i++)
for (int i = 0; i < magnitude; i++)
{
this_arg_number /= (ecma_number_t) radix;
}
}
else
else if (exponent < 0)
{
for (int i = 0; i < scale; i++)
for (int i = 0; i < magnitude; i++)
{
this_arg_number *= (ecma_number_t) radix;
}
}
/* Split the number into an integer and a fractional part, since we have to handle them separately. */
uint64_t whole = (uint64_t) this_arg_number;
ecma_number_t fraction = this_arg_number - (ecma_number_t) whole;
bool should_round = false;
if (!ecma_number_is_zero (fraction) && is_scale_negative)
if (!ecma_number_is_zero (fraction) && exponent >= 0)
{
/* Add one extra digit for rounding. */
buff_size++;
/*
* If the exponent is non-negative, and we get a non-zero fractional part, that means
* the normalization might have introduced a small error, in which case we have to correct it by rounding.
* We'll add one extra significant digit which we will later use to round.
*/
required_digits += 1;
should_round = true;
}
/* Get the total required buffer size and allocate the buffer. */
buff_size += required_digits;
JMEM_DEFINE_LOCAL_ARRAY (buff, buff_size, lit_utf8_byte_t);
int buff_index = 0;
/* Calculate digits for whole part. */
while (whole > 0)
{
JERRY_ASSERT (buff_index < buff_size && buff_index < required_digits);
buff[buff_index++] = (lit_utf8_byte_t) (whole % radix);
whole /= radix;
}
/* Calculate where we have to put the radix point. */
int point = is_scale_negative ? buff_index + scale : buff_index - scale;
/* Reverse the digits, since they are backwards. */
/* The digits are backwards, we need to reverse them. */
for (int i = 0; i < buff_index / 2; i++)
{
lit_utf8_byte_t swap = buff[i];
@ -357,20 +399,26 @@ ecma_builtin_number_prototype_object_to_string (ecma_value_t this_arg, /**< this
buff[buff_index - i - 1] = swap;
}
int required_digits = buff_size;
if (is_negative)
/*
* Calculate where we have to put the radix point relative to the beginning of
* the new digits. If the exponent is non-negative this will be right after the number.
*/
int point = exponent >= 0 ? magnitude + 1: buff_index - magnitude;
if (point < 0)
{
required_digits--;
/*
* In this case the radix point will be before the first digit,
* so we need to leave space for leading zeros.
*/
JERRY_ASSERT (exponent < 0);
required_digits += point;
}
if (!is_scale_negative)
{
/* Leave space for leading zeros / radix point. */
required_digits -= scale + 1;
}
JERRY_ASSERT (required_digits <= buff_size);
/* Calculate digits for fractional part. */
while (buff_index < required_digits && (fraction != 0 || is_scale_negative))
while (buff_index < required_digits)
{
fraction *= (ecma_number_t) radix;
lit_utf8_byte_t digit = (lit_utf8_byte_t) floor (fraction);
@ -381,31 +429,35 @@ ecma_builtin_number_prototype_object_to_string (ecma_value_t this_arg, /**< this
if (should_round)
{
/* Round off last digit. */
if (buff[buff_index - 1] > radix / 2)
{
buff[buff_index - 2]++;
}
/* Consume last digit for rounding. */
buff_index--;
/* Propagate carry. */
for (int i = buff_index - 1; i > 0 && buff[i] >= radix; i--)
if (buff[buff_index] > radix / 2)
{
buff[i] = (lit_utf8_byte_t) (buff[i] - radix);
buff[i - 1]++;
}
/* We should be rounding up. */
buff[buff_index - 1]++;
/* Carry propagated over the whole number, need to add a leading digit. */
if (buff[0] >= radix)
{
memmove (buff + 1, buff, (size_t) buff_index);
buff_index++;
buff[0] = 1;
/* Propagate carry forward in the digits. */
for (int i = buff_index - 1; i > 0 && buff[i] >= radix; i--)
{
buff[i] = (lit_utf8_byte_t) (buff[i] - radix);
buff[i - 1]++;
}
if (buff[0] >= radix)
{
/*
* Carry propagated over the whole number, we need to add a new leading digit.
* We can use the place of the original rounded digit, we just need to shift everything
* right by one.
*/
memmove (buff + 1, buff, (size_t) buff_index);
buff_index++;
buff[0] = 1;
}
}
}
/* Remove trailing zeros from fraction. */
/* Remove trailing zeros. */
while (buff_index - 1 > point && buff[buff_index - 1] == 0)
{
buff_index--;
@ -414,14 +466,17 @@ ecma_builtin_number_prototype_object_to_string (ecma_value_t this_arg, /**< this
/* Add leading zeros in case place of radix point is negative. */
if (point <= 0)
{
memmove (buff - point + 1, buff, (size_t) buff_index);
buff_index += -point + 1;
/* We will have 'point' amount of zeros after the radix point, and +1 before. */
int zero_count = -point + 1;
memmove (buff + zero_count, buff, (size_t) buff_index);
buff_index += zero_count;
for (int i = 0; i < -point + 1; i++)
for (int i = 0; i < zero_count; i++)
{
buff[i] = 0;
}
/* We now need to place the radix point after the first zero. */
point = 1;
}
@ -440,11 +495,11 @@ ecma_builtin_number_prototype_object_to_string (ecma_value_t this_arg, /**< this
}
/* Add negative sign if necessary. */
if (is_negative)
if (is_number_negative)
{
memmove (buff + 1, buff, (size_t) buff_index);
buff_index++;
buff[0] = '-';
buff_index++;
}
JERRY_ASSERT (buff_index <= buff_size);

2
tests/jerry/number-prototype-to-string.js
View File

@ -90,7 +90,7 @@ assert ((-0x100000000000061).toString(16) === "-100000000000060");
assert((123400).toString(new Number(16)) === "1e208");
assert(65535.9.toString(3) === "10022220020.220022002200220022002210211012200000110221");
assert(65535.9.toString(3) === "10022220020.2200220022002200220022102110122000001102212");
var digit_chars = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',