doc PG 17 relnotes: add FETCH_COUNT item

[pgsql.git] / src / common / f2s.c

/*---------------------------------------------------------------------------
 *
 * Ryu floating-point output for single precision.
 *
 * Portions Copyright (c) 2018-2024, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *        src/common/f2s.c
 *
 * This is a modification of code taken from github.com/ulfjack/ryu under the
 * terms of the Boost license (not the Apache license). The original copyright
 * notice follows:
 *
 * Copyright 2018 Ulf Adams
 *
 * The contents of this file may be used under the terms of the Apache
 * License, Version 2.0.
 *
 *     (See accompanying file LICENSE-Apache or copy at
 *      http://www.apache.org/licenses/LICENSE-2.0)
 *
 * Alternatively, the contents of this file may be used under the terms of the
 * Boost Software License, Version 1.0.
 *
 *     (See accompanying file LICENSE-Boost or copy at
 *      https://www.boost.org/LICENSE_1_0.txt)
 *
 * Unless required by applicable law or agreed to in writing, this software is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.
 *
 *---------------------------------------------------------------------------
 */

#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif

#include "common/shortest_dec.h"
#include "digit_table.h"
#include "ryu_common.h"

#define FLOAT_MANTISSA_BITS 23
#define FLOAT_EXPONENT_BITS 8
#define FLOAT_BIAS 127

/*
 * This table is generated (by the upstream) by PrintFloatLookupTable,
 * and modified (by us) to add UINT64CONST.
 */
#define FLOAT_POW5_INV_BITCOUNT 59
static const uint64 FLOAT_POW5_INV_SPLIT[31] = {
        UINT64CONST(576460752303423489), UINT64CONST(461168601842738791), UINT64CONST(368934881474191033), UINT64CONST(295147905179352826),
        UINT64CONST(472236648286964522), UINT64CONST(377789318629571618), UINT64CONST(302231454903657294), UINT64CONST(483570327845851670),
        UINT64CONST(386856262276681336), UINT64CONST(309485009821345069), UINT64CONST(495176015714152110), UINT64CONST(396140812571321688),
        UINT64CONST(316912650057057351), UINT64CONST(507060240091291761), UINT64CONST(405648192073033409), UINT64CONST(324518553658426727),
        UINT64CONST(519229685853482763), UINT64CONST(415383748682786211), UINT64CONST(332306998946228969), UINT64CONST(531691198313966350),
        UINT64CONST(425352958651173080), UINT64CONST(340282366920938464), UINT64CONST(544451787073501542), UINT64CONST(435561429658801234),
        UINT64CONST(348449143727040987), UINT64CONST(557518629963265579), UINT64CONST(446014903970612463), UINT64CONST(356811923176489971),
        UINT64CONST(570899077082383953), UINT64CONST(456719261665907162), UINT64CONST(365375409332725730)
};
#define FLOAT_POW5_BITCOUNT 61
static const uint64 FLOAT_POW5_SPLIT[47] = {
        UINT64CONST(1152921504606846976), UINT64CONST(1441151880758558720), UINT64CONST(1801439850948198400), UINT64CONST(2251799813685248000),
        UINT64CONST(1407374883553280000), UINT64CONST(1759218604441600000), UINT64CONST(2199023255552000000), UINT64CONST(1374389534720000000),
        UINT64CONST(1717986918400000000), UINT64CONST(2147483648000000000), UINT64CONST(1342177280000000000), UINT64CONST(1677721600000000000),
        UINT64CONST(2097152000000000000), UINT64CONST(1310720000000000000), UINT64CONST(1638400000000000000), UINT64CONST(2048000000000000000),
        UINT64CONST(1280000000000000000), UINT64CONST(1600000000000000000), UINT64CONST(2000000000000000000), UINT64CONST(1250000000000000000),
        UINT64CONST(1562500000000000000), UINT64CONST(1953125000000000000), UINT64CONST(1220703125000000000), UINT64CONST(1525878906250000000),
        UINT64CONST(1907348632812500000), UINT64CONST(1192092895507812500), UINT64CONST(1490116119384765625), UINT64CONST(1862645149230957031),
        UINT64CONST(1164153218269348144), UINT64CONST(1455191522836685180), UINT64CONST(1818989403545856475), UINT64CONST(2273736754432320594),
        UINT64CONST(1421085471520200371), UINT64CONST(1776356839400250464), UINT64CONST(2220446049250313080), UINT64CONST(1387778780781445675),
        UINT64CONST(1734723475976807094), UINT64CONST(2168404344971008868), UINT64CONST(1355252715606880542), UINT64CONST(1694065894508600678),
        UINT64CONST(2117582368135750847), UINT64CONST(1323488980084844279), UINT64CONST(1654361225106055349), UINT64CONST(2067951531382569187),
        UINT64CONST(1292469707114105741), UINT64CONST(1615587133892632177), UINT64CONST(2019483917365790221)
};

static inline uint32
pow5Factor(uint32 value)
{
        uint32          count = 0;

        for (;;)
        {
                Assert(value != 0);
                const uint32 q = value / 5;
                const uint32 r = value % 5;

                if (r != 0)
                        break;

                value = q;
                ++count;
        }
        return count;
}

/*  Returns true if value is divisible by 5^p. */
static inline bool
multipleOfPowerOf5(const uint32 value, const uint32 p)
{
        return pow5Factor(value) >= p;
}

/*  Returns true if value is divisible by 2^p. */
static inline bool
multipleOfPowerOf2(const uint32 value, const uint32 p)
{
        /* return __builtin_ctz(value) >= p; */
        return (value & ((1u << p) - 1)) == 0;
}

/*
 * It seems to be slightly faster to avoid uint128_t here, although the
 * generated code for uint128_t looks slightly nicer.
 */
static inline uint32
mulShift(const uint32 m, const uint64 factor, const int32 shift)
{
        /*
         * The casts here help MSVC to avoid calls to the __allmul library
         * function.
         */
        const uint32 factorLo = (uint32) (factor);
        const uint32 factorHi = (uint32) (factor >> 32);
        const uint64 bits0 = (uint64) m * factorLo;
        const uint64 bits1 = (uint64) m * factorHi;

        Assert(shift > 32);

#ifdef RYU_32_BIT_PLATFORM

        /*
         * On 32-bit platforms we can avoid a 64-bit shift-right since we only
         * need the upper 32 bits of the result and the shift value is > 32.
         */
        const uint32 bits0Hi = (uint32) (bits0 >> 32);
        uint32          bits1Lo = (uint32) (bits1);
        uint32          bits1Hi = (uint32) (bits1 >> 32);

        bits1Lo += bits0Hi;
        bits1Hi += (bits1Lo < bits0Hi);

        const int32 s = shift - 32;

        return (bits1Hi << (32 - s)) | (bits1Lo >> s);

#else                                                   /* RYU_32_BIT_PLATFORM */

        const uint64 sum = (bits0 >> 32) + bits1;
        const uint64 shiftedSum = sum >> (shift - 32);

        Assert(shiftedSum <= PG_UINT32_MAX);
        return (uint32) shiftedSum;

#endif                                                  /* RYU_32_BIT_PLATFORM */
}

static inline uint32
mulPow5InvDivPow2(const uint32 m, const uint32 q, const int32 j)
{
        return mulShift(m, FLOAT_POW5_INV_SPLIT[q], j);
}

static inline uint32
mulPow5divPow2(const uint32 m, const uint32 i, const int32 j)
{
        return mulShift(m, FLOAT_POW5_SPLIT[i], j);
}

static inline uint32
decimalLength(const uint32 v)
{
        /* Function precondition: v is not a 10-digit number. */
        /* (9 digits are sufficient for round-tripping.) */
        Assert(v < 1000000000);
        if (v >= 100000000)
        {
                return 9;
        }
        if (v >= 10000000)
        {
                return 8;
        }
        if (v >= 1000000)
        {
                return 7;
        }
        if (v >= 100000)
        {
                return 6;
        }
        if (v >= 10000)
        {
                return 5;
        }
        if (v >= 1000)
        {
                return 4;
        }
        if (v >= 100)
        {
                return 3;
        }
        if (v >= 10)
        {
                return 2;
        }
        return 1;
}

/*  A floating decimal representing m * 10^e. */
typedef struct floating_decimal_32
{
        uint32          mantissa;
        int32           exponent;
} floating_decimal_32;

static inline floating_decimal_32
f2d(const uint32 ieeeMantissa, const uint32 ieeeExponent)
{
        int32           e2;
        uint32          m2;

        if (ieeeExponent == 0)
        {
                /* We subtract 2 so that the bounds computation has 2 additional bits. */
                e2 = 1 - FLOAT_BIAS - FLOAT_MANTISSA_BITS - 2;
                m2 = ieeeMantissa;
        }
        else
        {
                e2 = ieeeExponent - FLOAT_BIAS - FLOAT_MANTISSA_BITS - 2;
                m2 = (1u << FLOAT_MANTISSA_BITS) | ieeeMantissa;
        }

#if STRICTLY_SHORTEST
        const bool      even = (m2 & 1) == 0;
        const bool      acceptBounds = even;
#else
        const bool      acceptBounds = false;
#endif

        /* Step 2: Determine the interval of legal decimal representations. */
        const uint32 mv = 4 * m2;
        const uint32 mp = 4 * m2 + 2;

        /* Implicit bool -> int conversion. True is 1, false is 0. */
        const uint32 mmShift = ieeeMantissa != 0 || ieeeExponent <= 1;
        const uint32 mm = 4 * m2 - 1 - mmShift;

        /* Step 3: Convert to a decimal power base using 64-bit arithmetic. */
        uint32          vr,
                                vp,
                                vm;
        int32           e10;
        bool            vmIsTrailingZeros = false;
        bool            vrIsTrailingZeros = false;
        uint8           lastRemovedDigit = 0;

        if (e2 >= 0)
        {
                const uint32 q = log10Pow2(e2);

                e10 = q;

                const int32 k = FLOAT_POW5_INV_BITCOUNT + pow5bits(q) - 1;
                const int32 i = -e2 + q + k;

                vr = mulPow5InvDivPow2(mv, q, i);
                vp = mulPow5InvDivPow2(mp, q, i);
                vm = mulPow5InvDivPow2(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.
                         */
                        const int32 l = FLOAT_POW5_INV_BITCOUNT + pow5bits(q - 1) - 1;

                        lastRemovedDigit = (uint8) (mulPow5InvDivPow2(mv, q - 1, -e2 + 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)
                        {
                                vrIsTrailingZeros = multipleOfPowerOf5(mv, q);
                        }
                        else if (acceptBounds)
                        {
                                vmIsTrailingZeros = multipleOfPowerOf5(mm, q);
                        }
                        else
                        {
                                vp -= multipleOfPowerOf5(mp, q);
                        }
                }
        }
        else
        {
                const uint32 q = log10Pow5(-e2);

                e10 = q + e2;

                const int32 i = -e2 - q;
                const int32 k = pow5bits(i) - FLOAT_POW5_BITCOUNT;
                int32           j = q - k;

                vr = mulPow5divPow2(mv, i, j);
                vp = mulPow5divPow2(mp, i, j);
                vm = mulPow5divPow2(mm, i, j);

                if (q != 0 && (vp - 1) / 10 <= vm / 10)
                {
                        j = q - 1 - (pow5bits(i + 1) - FLOAT_POW5_BITCOUNT);
                        lastRemovedDigit = (uint8) (mulPow5divPow2(mv, 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. */
                        vrIsTrailingZeros = true;
                        if (acceptBounds)
                        {
                                /*
                                 * mm = mv - 1 - mmShift, so it has 1 trailing 0 bit iff
                                 * mmShift == 1.
                                 */
                                vmIsTrailingZeros = mmShift == 1;
                        }
                        else
                        {
                                /*
                                 * mp = mv + 2, so it always has at least one trailing 0 bit.
                                 */
                                --vp;
                        }
                }
                else if (q < 31)
                {
                        /* TODO(ulfjack):Use a tighter bound here. */
                        vrIsTrailingZeros = multipleOfPowerOf2(mv, q - 1);
                }
        }

        /*
         * Step 4: Find the shortest decimal representation in the interval of
         * legal representations.
         */
        uint32          removed = 0;
        uint32          output;

        if (vmIsTrailingZeros || vrIsTrailingZeros)
        {
                /* General case, which happens rarely (~4.0%). */
                while (vp / 10 > vm / 10)
                {
                        vmIsTrailingZeros &= vm - (vm / 10) * 10 == 0;
                        vrIsTrailingZeros &= lastRemovedDigit == 0;
                        lastRemovedDigit = (uint8) (vr % 10);
                        vr /= 10;
                        vp /= 10;
                        vm /= 10;
                        ++removed;
                }
                if (vmIsTrailingZeros)
                {
                        while (vm % 10 == 0)
                        {
                                vrIsTrailingZeros &= lastRemovedDigit == 0;
                                lastRemovedDigit = (uint8) (vr % 10);
                                vr /= 10;
                                vp /= 10;
                                vm /= 10;
                                ++removed;
                        }
                }

                if (vrIsTrailingZeros && lastRemovedDigit == 5 && vr % 2 == 0)
                {
                        /* Round even if the exact number is .....50..0. */
                        lastRemovedDigit = 4;
                }

                /*
                 * We need to take vr + 1 if vr is outside bounds or we need to round
                 * up.
                 */
                output = vr + ((vr == vm && (!acceptBounds || !vmIsTrailingZeros)) || lastRemovedDigit >= 5);
        }
        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%
                 */
                while (vp / 10 > vm / 10)
                {
                        lastRemovedDigit = (uint8) (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.
                 */
                output = vr + (vr == vm || lastRemovedDigit >= 5);
        }

        const int32 exp = e10 + removed;

        floating_decimal_32 fd;

        fd.exponent = exp;
        fd.mantissa = output;
        return fd;
}

static inline int
to_chars_f(const floating_decimal_32 v, const uint32 olength, char *const result)
{
        /* Step 5: Print the decimal representation. */
        int                     index = 0;

        uint32          output = v.mantissa;
        int32           exp = v.exponent;

        /*----
         * On entry, mantissa * 10^exp is the result to be output.
         * Caller has already done the - sign if needed.
         *
         * We want to insert the point somewhere depending on the output length
         * and exponent, which might mean adding zeros:
         *
         *            exp  | format
         *            1+   |  ddddddddd000000
         *            0    |  ddddddddd
         *  -1 .. -len+1   |  dddddddd.d to d.ddddddddd
         *  -len ...       |  0.ddddddddd to 0.000dddddd
         */
        uint32          i = 0;
        int32           nexp = exp + olength;

        if (nexp <= 0)
        {
                /* -nexp is number of 0s to add after '.' */
                Assert(nexp >= -3);
                /* 0.000ddddd */
                index = 2 - nexp;
                /* copy 8 bytes rather than 5 to let compiler optimize */
                memcpy(result, "0.000000", 8);
        }
        else if (exp < 0)
        {
                /*
                 * dddd.dddd; leave space at the start and move the '.' in after
                 */
                index = 1;
        }
        else
        {
                /*
                 * We can save some code later by pre-filling with zeros. We know that
                 * there can be no more than 6 output digits in this form, otherwise
                 * we would not choose fixed-point output. memset 8 rather than 6
                 * bytes to let the compiler optimize it.
                 */
                Assert(exp < 6 && exp + olength <= 6);
                memset(result, '0', 8);
        }

        while (output >= 10000)
        {
                const uint32 c = output - 10000 * (output / 10000);
                const uint32 c0 = (c % 100) << 1;
                const uint32 c1 = (c / 100) << 1;

                output /= 10000;

                memcpy(result + index + olength - i - 2, DIGIT_TABLE + c0, 2);
                memcpy(result + index + olength - i - 4, DIGIT_TABLE + c1, 2);
                i += 4;
        }
        if (output >= 100)
        {
                const uint32 c = (output % 100) << 1;

                output /= 100;
                memcpy(result + index + olength - i - 2, DIGIT_TABLE + c, 2);
                i += 2;
        }
        if (output >= 10)
        {
                const uint32 c = output << 1;

                memcpy(result + index + olength - i - 2, DIGIT_TABLE + c, 2);
        }
        else
        {
                result[index] = (char) ('0' + output);
        }

        if (index == 1)
        {
                /*
                 * nexp is 1..6 here, representing the number of digits before the
                 * point. A value of 7+ is not possible because we switch to
                 * scientific notation when the display exponent reaches 6.
                 */
                Assert(nexp < 7);
                /* gcc only seems to want to optimize memmove for small 2^n */
                if (nexp & 4)
                {
                        memmove(result + index - 1, result + index, 4);
                        index += 4;
                }
                if (nexp & 2)
                {
                        memmove(result + index - 1, result + index, 2);
                        index += 2;
                }
                if (nexp & 1)
                {
                        result[index - 1] = result[index];
                }
                result[nexp] = '.';
                index = olength + 1;
        }
        else if (exp >= 0)
        {
                /* we supplied the trailing zeros earlier, now just set the length. */
                index = olength + exp;
        }
        else
        {
                index = olength + (2 - nexp);
        }

        return index;
}

static inline int
to_chars(const floating_decimal_32 v, const bool sign, char *const result)
{
        /* Step 5: Print the decimal representation. */
        int                     index = 0;

        uint32          output = v.mantissa;
        uint32          olength = decimalLength(output);
        int32           exp = v.exponent + olength - 1;

        if (sign)
                result[index++] = '-';

        /*
         * The thresholds for fixed-point output are chosen to match printf
         * defaults. Beware that both the code of to_chars_f and the value of
         * FLOAT_SHORTEST_DECIMAL_LEN are sensitive to these thresholds.
         */
        if (exp >= -4 && exp < 6)
                return to_chars_f(v, olength, result + index) + sign;

        /*
         * If v.exponent is exactly 0, we might have reached here via the small
         * integer fast path, in which case v.mantissa might contain trailing
         * (decimal) zeros. For scientific notation we need to move these zeros
         * into the exponent. (For fixed point this doesn't matter, which is why
         * we do this here rather than above.)
         *
         * Since we already calculated the display exponent (exp) above based on
         * the old decimal length, that value does not change here. Instead, we
         * just reduce the display length for each digit removed.
         *
         * If we didn't get here via the fast path, the raw exponent will not
         * usually be 0, and there will be no trailing zeros, so we pay no more
         * than one div10/multiply extra cost. We claw back half of that by
         * checking for divisibility by 2 before dividing by 10.
         */
        if (v.exponent == 0)
        {
                while ((output & 1) == 0)
                {
                        const uint32 q = output / 10;
                        const uint32 r = output - 10 * q;

                        if (r != 0)
                                break;
                        output = q;
                        --olength;
                }
        }

        /*----
         * Print the decimal digits.
         * The following code is equivalent to:
         *
         * for (uint32 i = 0; i < olength - 1; ++i) {
         *   const uint32 c = output % 10; output /= 10;
         *   result[index + olength - i] = (char) ('0' + c);
         * }
         * result[index] = '0' + output % 10;
         */
        uint32          i = 0;

        while (output >= 10000)
        {
                const uint32 c = output - 10000 * (output / 10000);
                const uint32 c0 = (c % 100) << 1;
                const uint32 c1 = (c / 100) << 1;

                output /= 10000;

                memcpy(result + index + olength - i - 1, DIGIT_TABLE + c0, 2);
                memcpy(result + index + olength - i - 3, DIGIT_TABLE + c1, 2);
                i += 4;
        }
        if (output >= 100)
        {
                const uint32 c = (output % 100) << 1;

                output /= 100;
                memcpy(result + index + olength - i - 1, DIGIT_TABLE + c, 2);
                i += 2;
        }
        if (output >= 10)
        {
                const uint32 c = output << 1;

                /*
                 * We can't use memcpy here: the decimal dot goes between these two
                 * digits.
                 */
                result[index + olength - i] = DIGIT_TABLE[c + 1];
                result[index] = DIGIT_TABLE[c];
        }
        else
        {
                result[index] = (char) ('0' + output);
        }

        /* Print decimal point if needed. */
        if (olength > 1)
        {
                result[index + 1] = '.';
                index += olength + 1;
        }
        else
        {
                ++index;
        }

        /* Print the exponent. */
        result[index++] = 'e';
        if (exp < 0)
        {
                result[index++] = '-';
                exp = -exp;
        }
        else
                result[index++] = '+';

        memcpy(result + index, DIGIT_TABLE + 2 * exp, 2);
        index += 2;

        return index;
}

static inline bool
f2d_small_int(const uint32 ieeeMantissa,
                          const uint32 ieeeExponent,
                          floating_decimal_32 *v)
{
        const int32 e2 = (int32) ieeeExponent - FLOAT_BIAS - FLOAT_MANTISSA_BITS;

        /*
         * Avoid using multiple "return false;" here since it tends to provoke the
         * compiler into inlining multiple copies of f2d, which is undesirable.
         */

        if (e2 >= -FLOAT_MANTISSA_BITS && e2 <= 0)
        {
                /*----
                 * Since 2^23 <= m2 < 2^24 and 0 <= -e2 <= 23:
                 *   1 <= f = m2 / 2^-e2 < 2^24.
                 *
                 * Test if the lower -e2 bits of the significand are 0, i.e. whether
                 * the fraction is 0. We can use ieeeMantissa here, since the implied
                 * 1 bit can never be tested by this; the implied 1 can only be part
                 * of a fraction if e2 < -FLOAT_MANTISSA_BITS which we already
                 * checked. (e.g. 0.5 gives ieeeMantissa == 0 and e2 == -24)
                 */
                const uint32 mask = (1U << -e2) - 1;
                const uint32 fraction = ieeeMantissa & mask;

                if (fraction == 0)
                {
                        /*----
                         * f is an integer in the range [1, 2^24).
                         * Note: mantissa might contain trailing (decimal) 0's.
                         * Note: since 2^24 < 10^9, there is no need to adjust
                         * decimalLength().
                         */
                        const uint32 m2 = (1U << FLOAT_MANTISSA_BITS) | ieeeMantissa;

                        v->mantissa = m2 >> -e2;
                        v->exponent = 0;
                        return true;
                }
        }

        return false;
}

/*
 * Store the shortest decimal representation of the given float as an
 * UNTERMINATED string in the caller's supplied buffer (which must be at least
 * FLOAT_SHORTEST_DECIMAL_LEN-1 bytes long).
 *
 * Returns the number of bytes stored.
 */
int
float_to_shortest_decimal_bufn(float f, char *result)
{
        /*
         * Step 1: Decode the floating-point number, and unify normalized and
         * subnormal cases.
         */
        const uint32 bits = float_to_bits(f);

        /* Decode bits into sign, mantissa, and exponent. */
        const bool      ieeeSign = ((bits >> (FLOAT_MANTISSA_BITS + FLOAT_EXPONENT_BITS)) & 1) != 0;
        const uint32 ieeeMantissa = bits & ((1u << FLOAT_MANTISSA_BITS) - 1);
        const uint32 ieeeExponent = (bits >> FLOAT_MANTISSA_BITS) & ((1u << FLOAT_EXPONENT_BITS) - 1);

        /* Case distinction; exit early for the easy cases. */
        if (ieeeExponent == ((1u << FLOAT_EXPONENT_BITS) - 1u) || (ieeeExponent == 0 && ieeeMantissa == 0))
        {
                return copy_special_str(result, ieeeSign, (ieeeExponent != 0), (ieeeMantissa != 0));
        }

        floating_decimal_32 v;
        const bool      isSmallInt = f2d_small_int(ieeeMantissa, ieeeExponent, &v);

        if (!isSmallInt)
        {
                v = f2d(ieeeMantissa, ieeeExponent);
        }

        return to_chars(v, ieeeSign, result);
}

/*
 * Store the shortest decimal representation of the given float as a
 * null-terminated string in the caller's supplied buffer (which must be at
 * least FLOAT_SHORTEST_DECIMAL_LEN bytes long).
 *
 * Returns the string length.
 */
int
float_to_shortest_decimal_buf(float f, char *result)
{
        const int       index = float_to_shortest_decimal_bufn(f, result);

        /* Terminate the string. */
        Assert(index < FLOAT_SHORTEST_DECIMAL_LEN);
        result[index] = '\0';
        return index;
}

/*
 * Return the shortest decimal representation as a null-terminated palloc'd
 * string (outside the backend, uses malloc() instead).
 *
 * Caller is responsible for freeing the result.
 */
char *
float_to_shortest_decimal(float f)
{
        char       *const result = (char *) palloc(FLOAT_SHORTEST_DECIMAL_LEN);

        float_to_shortest_decimal_buf(f, result);
        return result;
}