Improve Number.prototype.toString for radix other than 10 (#284)

- 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

Fixes: #242

Author: chqrlie

quickjs.c

@@ -10971,6 +10971,8 @@ static JSValue js_bigint_to_string(JSContext *ctx, JSValue val)
 }
 
 /* 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;
@@ -10982,15 +10984,20 @@ 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;
@@ -11238,6 +11245,80 @@ 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, JSValue val, BOOL is_ToPropertyKey)
 {
     uint32_t tag;
@@ -38557,8 +38638,16 @@ static JSValue js_number_toString(JSContext *ctx, JSValue 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);

v8.txt

@@ -799,113 +799,9 @@ Failure: expected <true> found <false>
 === number-string-index-call.js
 === number-tostring-add.js
 === number-tostring-big-integer.js
-Failure:
-expected:
-"314404114120101444444424000000000000000"
-found:
-"1.2345e+27"
 === number-tostring-func.js
-Failure: expected <"5a.1eb851eb852"> found <"90.12">
-Failure: expected <"0.1999999999999a"> found <"0.1">
-Failure: expected <"0.028f5c28f5c28f6"> found <"0.01">
-Failure: expected <"0.032617c1bda511a"> found <"0.0123">
-Failure: expected <"605f9f6dd18bc8000"> found <"111111111111111110000">
-Failure: expected <"3c3bc3a4a2f75c0000"> found <"1.1111111111111111e+21">
-Failure: expected <"25a55a46e5da9a00000"> found <"1.1111111111111111e+22">
-Failure: expected <"0.0000a7c5ac471b4788"> found <"0.00001">
-Failure: expected <"0.000010c6f7a0b5ed8d"> found <"0.000001">
-Failure: expected <"0.000001ad7f29abcaf48"> found <"1e-7">
-Failure: expected <"0.000002036565348d256"> found <"1.2e-7">
-Failure: expected <"0.0000021047ee22aa466"> found <"1.23e-7">
-Failure: expected <"0.0000002af31dc4611874"> found <"1e-8">
-Failure: expected <"0.000000338a23b87483be"> found <"1.2e-8">
-Failure: expected <"0.00000034d3fe36aaa0a2"> found <"1.23e-8">
-Failure: expected <"-5a.1eb851eb852"> found <"-90.12">
-Failure: expected <"-0.1999999999999a"> found <"-0.1">
-Failure: expected <"-0.028f5c28f5c28f6"> found <"-0.01">
-Failure: expected <"-0.032617c1bda511a"> found <"-0.0123">
-Failure: expected <"-605f9f6dd18bc8000"> found <"-111111111111111110000">
-Failure: expected <"-3c3bc3a4a2f75c0000"> found <"-1.1111111111111111e+21">
-Failure: expected <"-25a55a46e5da9a00000"> found <"-1.1111111111111111e+22">
-Failure: expected <"-0.0000a7c5ac471b4788"> found <"-0.00001">
-Failure: expected <"-0.000010c6f7a0b5ed8d"> found <"-0.000001">
-Failure: expected <"-0.000001ad7f29abcaf48"> found <"-1e-7">
-Failure: expected <"-0.000002036565348d256"> found <"-1.2e-7">
-Failure: expected <"-0.0000021047ee22aa466"> found <"-1.23e-7">
-Failure: expected <"-0.0000002af31dc4611874"> found <"-1e-8">
-Failure: expected <"-0.000000338a23b87483be"> found <"-1.2e-8">
-Failure: expected <"-0.00000034d3fe36aaa0a2"> found <"-1.23e-8">
-Failure: expected <"100000000000080"> found <"72057594037928060">
-Failure: expected <"1000000000000100"> found <"1152921504606847200">
-Failure: expected <"1000000000000000"> found <"1152921504606847000">
-Failure: expected <"1000000000000000"> found <"1152921504606847000">
-Failure:
-expected:
-"100000000000000000000000000000000000000000000000010000000"
-found:
-"72057594037928060"
-Failure: expected <"-100000000000080"> found <"-72057594037928060">
-Failure:
-expected:
-"-100000000000000000000000000000000000000000000000010000000"
-found:
-"-72057594037928060"
-Failure: expected <"8.8"> found <"8.5">
-Failure: expected <"-8.8"> found <"-8.5">
 === number-tostring-small.js
 === number-tostring.js
-Failure: expected <"5a.1eb851eb852"> found <"90.12">
-Failure: expected <"0.1999999999999a"> found <"0.1">
-Failure: expected <"0.028f5c28f5c28f6"> found <"0.01">
-Failure: expected <"0.032617c1bda511a"> found <"0.0123">
-Failure: expected <"605f9f6dd18bc8000"> found <"111111111111111110000">
-Failure: expected <"3c3bc3a4a2f75c0000"> found <"1.1111111111111111e+21">
-Failure: expected <"25a55a46e5da9a00000"> found <"1.1111111111111111e+22">
-Failure: expected <"0.0000a7c5ac471b4788"> found <"0.00001">
-Failure: expected <"0.000010c6f7a0b5ed8d"> found <"0.000001">
-Failure: expected <"0.000001ad7f29abcaf48"> found <"1e-7">
-Failure: expected <"0.000002036565348d256"> found <"1.2e-7">
-Failure: expected <"0.0000021047ee22aa466"> found <"1.23e-7">
-Failure: expected <"0.0000002af31dc4611874"> found <"1e-8">
-Failure: expected <"0.000000338a23b87483be"> found <"1.2e-8">
-Failure: expected <"0.00000034d3fe36aaa0a2"> found <"1.23e-8">
-Failure: expected <"-5a.1eb851eb852"> found <"-90.12">
-Failure: expected <"-0.1999999999999a"> found <"-0.1">
-Failure: expected <"-0.028f5c28f5c28f6"> found <"-0.01">
-Failure: expected <"-0.032617c1bda511a"> found <"-0.0123">
-Failure: expected <"-605f9f6dd18bc8000"> found <"-111111111111111110000">
-Failure: expected <"-3c3bc3a4a2f75c0000"> found <"-1.1111111111111111e+21">
-Failure: expected <"-25a55a46e5da9a00000"> found <"-1.1111111111111111e+22">
-Failure: expected <"-0.0000a7c5ac471b4788"> found <"-0.00001">
-Failure: expected <"-0.000010c6f7a0b5ed8d"> found <"-0.000001">
-Failure: expected <"-0.000001ad7f29abcaf48"> found <"-1e-7">
-Failure: expected <"-0.000002036565348d256"> found <"-1.2e-7">
-Failure: expected <"-0.0000021047ee22aa466"> found <"-1.23e-7">
-Failure: expected <"-0.0000002af31dc4611874"> found <"-1e-8">
-Failure: expected <"-0.000000338a23b87483be"> found <"-1.2e-8">
-Failure: expected <"-0.00000034d3fe36aaa0a2"> found <"-1.23e-8">
-Failure: expected <"100000000000080"> found <"72057594037928060">
-Failure: expected <"1000000000000100"> found <"1152921504606847200">
-Failure: expected <"1000000000000000"> found <"1152921504606847000">
-Failure: expected <"1000000000000000"> found <"1152921504606847000">
-Failure:
-expected:
-"100000000000000000000000000000000000000000000000010000000"
-found:
-"72057594037928060"
-Failure: expected <"-100000000000080"> found <"-72057594037928060">
-Failure:
-expected:
-"-100000000000000000000000000000000000000000000000010000000"
-found:
-"-72057594037928060"
-Failure: expected <"8.8"> found <"8.5">
-Failure: expected <"-8.8"> found <"-8.5">
-Failure: expected <"1.1"> found <"1.3333333333333333">
-Failure: expected <"11.1"> found <"4.333333333333333">
-Failure: expected <"0.01"> found <"0.1111111111111111">
-Failure: expected <"10000.01"> found <"81.11111111111111">
-Failure: expected <"0.0212010212010212010212010212010212"> found <"0.2857142857142857">
 === numops-fuzz-part1.js
 === numops-fuzz-part2.js
 === numops-fuzz-part3.js