ryu_common.h

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/*---------------------------------------------------------------------------
 *
 * Common routines for Ryu floating-point output.
 *
 * Portions Copyright (c) 2018-2024, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/common/ryu_common.h
 *
 * 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 RYU_COMMON_H
#define RYU_COMMON_H
 
/*
 * Upstream Ryu's output is always the shortest possible. But we adjust that
 * slightly to improve portability: we avoid outputting the exact midpoint
 * value between two representable floats, since that relies on the reader
 * getting the round-to-even rule correct, which seems to be the common
 * failure mode.
 *
 * Defining this to 1 would restore the upstream behavior.
 */
#define STRICTLY_SHORTEST 0
 
#if SIZEOF_SIZE_T < 8
#define RYU_32_BIT_PLATFORM
#endif
 
/*  Returns e == 0 ? 1 : ceil(log_2(5^e)). */
static inline uint32
pow5bits(const int32 e)
{
    /*
     * This approximation works up to the point that the multiplication
     * overflows at e = 3529.
     *
     * If the multiplication were done in 64 bits, it would fail at 5^4004
     * which is just greater than 2^9297.
     */
    Assert(e >= 0);
    Assert(e <= 3528);
    return ((((uint32) e) * 1217359) >> 19) + 1;
}
 
/*  Returns floor(log_10(2^e)). */
static inline int32
log10Pow2(const int32 e)
{
    /*
     * The first value this approximation fails for is 2^1651 which is just
     * greater than 10^297.
     */
    Assert(e >= 0);
    Assert(e <= 1650);
    return (int32) ((((uint32) e) * 78913) >> 18);
}
 
/*  Returns floor(log_10(5^e)). */
static inline int32
log10Pow5(const int32 e)
{
    /*
     * The first value this approximation fails for is 5^2621 which is just
     * greater than 10^1832.
     */
    Assert(e >= 0);
    Assert(e <= 2620);
    return (int32) ((((uint32) e) * 732923) >> 20);
}
 
static inline int
copy_special_str(char *const result, const bool sign, const bool exponent, const bool mantissa)
{
    if (mantissa)
    {
        memcpy(result, "NaN", 3);
        return 3;
    }
    if (sign)
    {
        result[0] = '-';
    }
    if (exponent)
    {
        memcpy(result + sign, "Infinity", 8);
        return sign + 8;
    }
    result[sign] = '0';
    return sign + 1;
}
 
static inline uint32
float_to_bits(const float f)
{
    uint32      bits = 0;
 
    memcpy(&bits, &f, sizeof(float));
    return bits;
}
 
static inline uint64
double_to_bits(const double d)
{
    uint64      bits = 0;
 
    memcpy(&bits, &d, sizeof(double));
    return bits;
}
 
#endif                          /* RYU_COMMON_H */