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Improve Number.prototype.toString for radix other than 10

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- fix the conversions for integers and exact fractions
- approximate approach for other cases.
- bypass floating point conversions for JS_TAG_INT values
- avoid divisions for base 10 integer conversions
This commit is contained in:
Charlie Gordon 2024-03-02 15:13:18 +01:00
parent a78d2cbf7c
commit 8d64731eb8
1 changed files with 98 additions and 9 deletions
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107
quickjs.c
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@ -11328,6 +11328,8 @@ static JSValue js_bigdecimal_to_string(JSContext *ctx, JSValueConst val)
#endif /* CONFIG_BIGNUM */
/* 2 <= base <= 36 */
static char const digits[36] = "0123456789abcdefghijklmnopqrstuvwxyz";
static char *i64toa(char *buf_end, int64_t n, unsigned int base)
{
char *q = buf_end;
@ -11339,15 +11341,20 @@ static char *i64toa(char *buf_end, int64_t n, unsigned int base)
n = -n;
}
*--q = '\0';
do {
digit = (uint64_t)n % base;
n = (uint64_t)n / base;
if (digit < 10)
digit += '0';
else
digit += 'a' - 10;
*--q = digit;
} while (n != 0);
if (base == 10) {
/* division by known base uses multiplication */
do {
digit = (uint64_t)n % 10;
n = (uint64_t)n / 10;
*--q = '0' + digit;
} while (n != 0);
} else {
do {
digit = (uint64_t)n % base;
n = (uint64_t)n / base;
*--q = digits[digit];
} while (n != 0);
}
if (is_neg)
*--q = '-';
return q;
@ -11595,6 +11602,80 @@ static JSValue js_dtoa(JSContext *ctx,
return JS_NewString(ctx, buf);
}
static JSValue js_dtoa_radix(JSContext *ctx, double d, int radix)
{
char buf[2200], *ptr, *ptr2;
/* d is finite */
int sign = d < 0;
int digit;
double frac, d0;
int64_t n0 = 0;
d = fabs(d);
d0 = trunc(d);
frac = d - d0;
ptr = buf + 1100;
*ptr = '\0';
if (d0 <= MAX_SAFE_INTEGER) {
int64_t n = n0 = (int64_t)d0;
while (n >= radix) {
digit = n % radix;
n = n / radix;
*--ptr = digits[digit];
}
*--ptr = digits[(int)n];
} else {
/* no decimals */
while (d0 >= radix) {
digit = fmod(d0, radix);
d0 = trunc(d0 / radix);
if (d0 >= MAX_SAFE_INTEGER)
digit = 0;
*--ptr = digits[digit];
}
*--ptr = digits[(int)d0];
goto done;
}
if (frac != 0) {
double log2_radix = log2(radix);
double prec = 1023 + 51; // handle subnormals
ptr2 = buf + 1100;
*ptr2++ = '.';
while (frac != 0 && n0 <= MAX_SAFE_INTEGER/2 && prec > 0) {
frac *= radix;
digit = trunc(frac);
frac -= digit;
*ptr2++ = digits[digit];
n0 = n0 * radix + digit;
prec -= log2_radix;
}
*ptr2 = '\0';
if (frac * radix >= radix / 2) {
char nine = digits[radix - 1];
// round to closest
while (ptr2[-1] == nine)
*--ptr2 = '\0';
if (ptr2[-1] == '.') {
*--ptr2 = '\0';
while (ptr2[-1] == nine)
*--ptr2 = '0';
}
if (ptr2 - 1 == ptr)
*--ptr = '1';
else
ptr2[-1] += 1;
} else {
while (ptr2[-1] == '0')
*--ptr2 = '\0';
if (ptr2[-1] == '.')
*--ptr2 = '\0';
}
}
done:
ptr[-1] = '-';
ptr -= sign;
return JS_NewString(ctx, ptr);
}
JSValue JS_ToStringInternal(JSContext *ctx, JSValueConst val, BOOL is_ToPropertyKey)
{
uint32_t tag;
@ -40975,8 +41056,16 @@ static JSValue js_number_toString(JSContext *ctx, JSValueConst this_val,
if (base < 0)
goto fail;
}
if (JS_VALUE_GET_TAG(val) == JS_TAG_INT) {
char buf1[70], *ptr;
ptr = i64toa(buf1 + sizeof(buf1), JS_VALUE_GET_INT(val), base);
return JS_NewString(ctx, ptr);
}
if (JS_ToFloat64Free(ctx, &d, val))
return JS_EXCEPTION;
if (base != 10 && isfinite(d)) {
return js_dtoa_radix(ctx, d, base);
}
return js_dtoa(ctx, d, base, 0, JS_DTOA_VAR_FORMAT);
fail:
JS_FreeValue(ctx, val);