Faster integer formatting

ext/json/ext/fbuffer/fbuffer.h

@@ -3,6 +3,7 @@
 
 #include "ruby.h"
 #include "ruby/encoding.h"
+#include "../vendor/jeaiii-ltoa.h"
 
 /* shims */
 /* This is the fallback definition from Ruby 3.4 */
@@ -150,6 +151,13 @@ static void fbuffer_append(FBuffer *fb, const char *newstr, unsigned long len)
     }
 }
 
+/* Appends a character into a buffer. The buffer needs to have sufficient capacity, via fbuffer_inc_capa(...). */
+static inline void fbuffer_append_reserved_char(FBuffer *fb, char chr)
+{
+    fb->ptr[fb->len] = chr;
+    fb->len += 1;
+}
+
 static void fbuffer_append_str(FBuffer *fb, VALUE str)
 {
     const char *newstr = StringValuePtr(str);
@@ -167,25 +175,48 @@ static inline void fbuffer_append_char(FBuffer *fb, char newchr)
     fb->len++;
 }
 
-static long fltoa(long number, char *buf)
+static inline char *fbuffer_cursor(FBuffer *fb)
+{
+    return fb->ptr + fb->len;
+}
+
+static inline void fbuffer_advance_to(FBuffer *fb, char *end)
 {
-    static const char digits[] = "0123456789";
-    long sign = number;
-    char* tmp = buf;
-
-    if (sign < 0) number = -number;
-    do *tmp-- = digits[number % 10]; while (number /= 10);
-    if (sign < 0) *tmp-- = '-';
-    return buf - tmp;
+    fb->len = end - fb->ptr;
 }
 
-#define LONG_BUFFER_SIZE 20
+/*
+ * Appends the decimal string representation of \a number into the buffer.
+ */
 static void fbuffer_append_long(FBuffer *fb, long number)
 {
-    char buf[LONG_BUFFER_SIZE];
-    char *buffer_end = buf + LONG_BUFFER_SIZE;
-    long len = fltoa(number, buffer_end - 1);
-    fbuffer_append(fb, buffer_end - len, len);
+    /*
+     * The jeaiii_ultoa() function produces digits left-to-right,
+     * allowing us to write directly into the buffer, but we don't know
+     * the number of resulting characters.
+     *
+     * We do know, however, that the `number` argument is always in the
+     * range 0xc000000000000000 to 0x3fffffffffffffff, or, in decimal, 
+     * -4611686018427387904 to 4611686018427387903. The max number of chars
+     * generated is therefore 20 (including a potential sign character).
+     */
+
+    static const int MAX_CHARS_FOR_LONG = 20;
+
+    fbuffer_inc_capa(fb, MAX_CHARS_FOR_LONG);
+
+    if (number < 0) {
+        fbuffer_append_reserved_char(fb, '-');
+
+        /* 
+         * Since number is always > LONG_MIN, `-number` will not overflow
+         * and is always the positive abs() value.
+         */
+        number = -number;
+    }
+
+    char *end = jeaiii_ultoa(fbuffer_cursor(fb), number);
+    fbuffer_advance_to(fb, end);
 }
 
 static VALUE fbuffer_finalize(FBuffer *fb)

ext/json/ext/generator/depend

@@ -1,2 +1,3 @@
 generator.o: generator.c $(srcdir)/../fbuffer/fbuffer.h
 generator.o: generator.c $(srcdir)/../vendor/fpconv.c
+generator.o: generator.c $(srcdir)/../vendor/jeaiii-ltoa.h

ext/json/ext/vendor/jeaiii-ltoa.h

@@ -0,0 +1,277 @@
+/*
+
+This file is released under the terms of the MIT License. It is based on the
+work of James Edward Anhalt III, with the original license listed below.
+
+MIT License
+
+Copyright (c) 2024,2025 Enrico Thierbach - https://github.com/radiospiel
+Copyright (c) 2022 James Edward Anhalt III - https://github.com/jeaiii/itoa
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
+#ifndef JEAIII_TO_TEXT_H_
+#define JEAIII_TO_TEXT_H_
+
+#include <stdint.h>
+
+typedef uint_fast32_t u32_t;
+typedef uint_fast64_t u64_t;
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wshorten-64-to-32"
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wmissing-braces"
+
+#define u32(x) ((u32_t)(x))
+#define u64(x) ((u64_t)(x))
+
+struct digit_pair
+{
+    char dd[2];
+};
+
+static const struct digit_pair *digits_dd = (struct digit_pair *)(
+    "00" "01" "02" "03" "04" "05" "06" "07" "08" "09"
+    "10" "11" "12" "13" "14" "15" "16" "17" "18" "19"
+    "20" "21" "22" "23" "24" "25" "26" "27" "28" "29"
+    "30" "31" "32" "33" "34" "35" "36" "37" "38" "39"
+    "40" "41" "42" "43" "44" "45" "46" "47" "48" "49"
+    "50" "51" "52" "53" "54" "55" "56" "57" "58" "59"
+    "60" "61" "62" "63" "64" "65" "66" "67" "68" "69"
+    "70" "71" "72" "73" "74" "75" "76" "77" "78" "79"
+    "80" "81" "82" "83" "84" "85" "86" "87" "88" "89"
+    "90" "91" "92" "93" "94" "95" "96" "97" "98" "99"
+);
+
+static const struct digit_pair *digits_fd = (struct digit_pair *)(
+    "0_" "1_" "2_" "3_" "4_" "5_" "6_" "7_" "8_" "9_"
+    "10" "11" "12" "13" "14" "15" "16" "17" "18" "19"
+    "20" "21" "22" "23" "24" "25" "26" "27" "28" "29"
+    "30" "31" "32" "33" "34" "35" "36" "37" "38" "39"
+    "40" "41" "42" "43" "44" "45" "46" "47" "48" "49"
+    "50" "51" "52" "53" "54" "55" "56" "57" "58" "59"
+    "60" "61" "62" "63" "64" "65" "66" "67" "68" "69"
+    "70" "71" "72" "73" "74" "75" "76" "77" "78" "79"
+    "80" "81" "82" "83" "84" "85" "86" "87" "88" "89"
+    "90" "91" "92" "93" "94" "95" "96" "97" "98" "99"
+);
+
+static const u64_t mask24 = (u64(1) << 24) - 1;
+static const u64_t mask32 = (u64(1) << 32) - 1;
+static const u64_t mask57 = (u64(1) << 57) - 1;
+
+#define COPY(buffer, digits) memcpy(buffer, &(digits), sizeof(struct digit_pair))
+
+static char *
+jeaiii_ultoa(char *b, u64_t n)
+{
+    if (n < u32(1e2)) {
+        COPY(b, digits_fd[n]);
+        return n < 10 ? b + 1 : b + 2;
+    }
+
+    if (n < u32(1e6)) {
+        if (n < u32(1e4)) {
+            u32_t f0 = u32(10 * (1 << 24) / 1e3 + 1) * n;
+            COPY(b, digits_fd[f0 >> 24]);
+
+            b -= n < u32(1e3);
+            u32_t f2 = (f0 & mask24) * 100;
+            COPY(b + 2, digits_dd[f2 >> 24]);
+
+            return b + 4;
+        }
+
+        u64_t f0 = u64(10 * (1ull << 32ull)/ 1e5 + 1) * n;
+        COPY(b, digits_fd[f0 >> 32]);
+
+        b -= n < u32(1e5);
+        u64_t f2 = (f0 & mask32) * 100;
+        COPY(b + 2, digits_dd[f2 >> 32]);
+
+        u64_t f4 = (f2 & mask32) * 100;
+        COPY(b + 4, digits_dd[f4 >> 32]);
+        return b + 6;
+    }
+
+    if (n < u64(1ull << 32ull)) {
+        if (n < u32(1e8)) {
+            u64_t f0 = u64(10 * (1ull << 48ull) / 1e7 + 1) * n >> 16;
+            COPY(b, digits_fd[f0 >> 32]);
+
+            b -= n < u32(1e7);
+            u64_t f2 = (f0 & mask32) * 100;
+            COPY(b + 2, digits_dd[f2 >> 32]);
+
+            u64_t f4 = (f2 & mask32) * 100;
+            COPY(b + 4, digits_dd[f4 >> 32]);
+
+            u64_t f6 = (f4 & mask32) * 100;
+            COPY(b + 6, digits_dd[f6 >> 32]);
+
+            return b + 8;
+        }
+
+        u64_t f0 = u64(10 * (1ull << 57ull) / 1e9 + 1) * n;
+        COPY(b, digits_fd[f0 >> 57]);
+
+        b -= n < u32(1e9);
+        u64_t f2 = (f0 & mask57) * 100;
+        COPY(b + 2, digits_dd[f2 >> 57]);
+
+        u64_t f4 = (f2 & mask57) * 100;
+        COPY(b + 4, digits_dd[f4 >> 57]);
+
+        u64_t f6 = (f4 & mask57) * 100;
+        COPY(b + 6, digits_dd[f6 >> 57]);
+
+        u64_t f8 = (f6 & mask57) * 100;
+        COPY(b + 8, digits_dd[f8 >> 57]);
+
+        return b + 10;
+    }
+
+    // if we get here U must be u64 but some compilers don't know that, so reassign n to a u64 to avoid warnings
+    u32_t z = n % u32(1e8);
+    u64_t u = n / u32(1e8);
+
+    if (u < u32(1e2)) {
+        // u can't be 1 digit (if u < 10 it would have been handled above as a 9 digit 32bit number)
+        COPY(b, digits_dd[u]);
+        b += 2;
+    }
+    else if (u < u32(1e6)) {
+        if (u < u32(1e4)) {
+            u32_t f0 = u32(10 * (1 << 24) / 1e3 + 1) * u;
+            COPY(b, digits_fd[f0 >> 24]);
+
+            b -= u < u32(1e3);
+            u32_t f2 = (f0 & mask24) * 100;
+            COPY(b + 2, digits_dd[f2 >> 24]);
+            b += 4;
+        }
+        else {
+            u64_t f0 = u64(10 * (1ull << 32ull) / 1e5 + 1) * u;
+            COPY(b, digits_fd[f0 >> 32]);
+
+            b -= u < u32(1e5);
+            u64_t f2 = (f0 & mask32) * 100;
+            COPY(b + 2, digits_dd[f2 >> 32]);
+
+            u64_t f4 = (f2 & mask32) * 100;
+            COPY(b + 4, digits_dd[f4 >> 32]);
+            b += 6;
+        }
+    }
+    else if (u < u32(1e8)) {
+        u64_t f0 = u64(10 * (1ull << 48ull) / 1e7 + 1) * u >> 16;
+        COPY(b, digits_fd[f0 >> 32]);
+
+        b -= u < u32(1e7);
+        u64_t f2 = (f0 & mask32) * 100;
+        COPY(b + 2, digits_dd[f2 >> 32]);
+
+        u64_t f4 = (f2 & mask32) * 100;
+        COPY(b + 4, digits_dd[f4 >> 32]);
+
+        u64_t f6 = (f4 & mask32) * 100;
+        COPY(b + 6, digits_dd[f6 >> 32]);
+
+        b += 8;
+    }
+    else if (u < u64(1ull << 32ull)) {
+        u64_t f0 = u64(10 * (1ull << 57ull) / 1e9 + 1) * u;
+        COPY(b, digits_fd[f0 >> 57]);
+
+        b -= u < u32(1e9);
+        u64_t f2 = (f0 & mask57) * 100;
+        COPY(b + 2, digits_dd[f2 >> 57]);
+
+        u64_t f4 = (f2 & mask57) * 100;
+        COPY(b + 4, digits_dd[f4 >> 57]);
+
+        u64_t f6 = (f4 & mask57) * 100;
+        COPY(b + 6, digits_dd[f6 >> 57]);
+
+        u64_t f8 = (f6 & mask57) * 100;
+        COPY(b + 8, digits_dd[f8 >> 57]);
+        b += 10;
+    }
+    else {
+        u32_t y = u % u32(1e8);
+        u /= u32(1e8);
+
+        // u is 2, 3, or 4 digits (if u < 10 it would have been handled above)
+        if (u < u32(1e2)) {
+            COPY(b, digits_dd[u]);
+            b += 2;
+        }
+        else {
+            u32_t f0 = u32(10 * (1 << 24) / 1e3 + 1) * u;
+            COPY(b, digits_fd[f0 >> 24]);
+
+            b -= u < u32(1e3);
+            u32_t f2 = (f0 & mask24) * 100;
+            COPY(b + 2, digits_dd[f2 >> 24]);
+
+            b += 4;
+        }
+        // do 8 digits
+        u64_t f0 = (u64((1ull << 48ull) / 1e6 + 1) * y >> 16) + 1;
+        COPY(b, digits_dd[f0 >> 32]);
+
+        u64_t f2 = (f0 & mask32) * 100;
+        COPY(b + 2, digits_dd[f2 >> 32]);
+
+        u64_t f4 = (f2 & mask32) * 100;
+        COPY(b + 4, digits_dd[f4 >> 32]);
+
+        u64_t f6 = (f4 & mask32) * 100;
+        COPY(b + 6, digits_dd[f6 >> 32]);
+        b += 8;
+    }
+
+    // do 8 digits
+    u64_t f0 = (u64((1ull << 48ull) / 1e6 + 1) * z >> 16) + 1;
+    COPY(b, digits_dd[f0 >> 32]);
+
+    u64_t f2 = (f0 & mask32) * 100;
+    COPY(b + 2, digits_dd[f2 >> 32]);
+
+    u64_t f4 = (f2 & mask32) * 100;
+    COPY(b + 4, digits_dd[f4 >> 32]);
+
+    u64_t f6 = (f4 & mask32) * 100;
+    COPY(b + 6, digits_dd[f6 >> 32]);
+
+    return b + 8;
+}
+
+#undef u32
+#undef u64
+#undef COPY
+
+#pragma clang diagnostic pop
+#pragma GCC diagnostic pop
+
+#endif // JEAIII_TO_TEXT_H_
+

test/json/json_generator_test.rb

@@ -707,4 +707,16 @@ def test_json_generate_float
         assert_equal expected, value.to_json
       end
   end
+
+  def test_numbers_of_various_sizes
+    numbers = [
+      0, 1, -1, 9, -9, 13, -13, 91, -91, 513, -513, 7513, -7513,
+      17591, -17591, -4611686018427387904, 4611686018427387903,
+      2**62, 2**63, 2**64, -(2**62), -(2**63), -(2**64)
+    ]
+
+    numbers.each do |number|
+      assert_equal "[#{number}]", JSON.generate([number])
+    end
+  end
 end