d2s_intrinsics.h

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/*---------------------------------------------------------------------------
 *
 * Ryu floating-point output for double precision.
 *
 * Portions Copyright (c) 2018-2024, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/common/d2s_intrinsics.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_D2S_INTRINSICS_H
#define RYU_D2S_INTRINSICS_H
 
#if defined(HAS_64_BIT_INTRINSICS)
 
#include <intrin.h>
 
static inline uint64
umul128(const uint64 a, const uint64 b, uint64 *const productHi)
{
    return _umul128(a, b, productHi);
}
 
static inline uint64
shiftright128(const uint64 lo, const uint64 hi, const uint32 dist)
{
    /*
     * For the __shiftright128 intrinsic, the shift value is always modulo 64.
     * In the current implementation of the double-precision version of Ryu,
     * the shift value is always < 64. (In the case RYU_OPTIMIZE_SIZE == 0,
     * the shift value is in the range [49, 58]. Otherwise in the range [2,
     * 59].) Check this here in case a future change requires larger shift
     * values. In this case this function needs to be adjusted.
     */
    Assert(dist < 64);
    return __shiftright128(lo, hi, (unsigned char) dist);
}
 
#else                           /* defined(HAS_64_BIT_INTRINSICS) */
 
static inline uint64
umul128(const uint64 a, const uint64 b, uint64 *const productHi)
{
    /*
     * The casts here help MSVC to avoid calls to the __allmul library
     * function.
     */
    const uint32 aLo = (uint32) a;
    const uint32 aHi = (uint32) (a >> 32);
    const uint32 bLo = (uint32) b;
    const uint32 bHi = (uint32) (b >> 32);
 
    const uint64 b00 = (uint64) aLo * bLo;
    const uint64 b01 = (uint64) aLo * bHi;
    const uint64 b10 = (uint64) aHi * bLo;
    const uint64 b11 = (uint64) aHi * bHi;
 
    const uint32 b00Lo = (uint32) b00;
    const uint32 b00Hi = (uint32) (b00 >> 32);
 
    const uint64 mid1 = b10 + b00Hi;
    const uint32 mid1Lo = (uint32) (mid1);
    const uint32 mid1Hi = (uint32) (mid1 >> 32);
 
    const uint64 mid2 = b01 + mid1Lo;
    const uint32 mid2Lo = (uint32) (mid2);
    const uint32 mid2Hi = (uint32) (mid2 >> 32);
 
    const uint64 pHi = b11 + mid1Hi + mid2Hi;
    const uint64 pLo = ((uint64) mid2Lo << 32) + b00Lo;
 
    *productHi = pHi;
    return pLo;
}
 
static inline uint64
shiftright128(const uint64 lo, const uint64 hi, const uint32 dist)
{
    /* We don't need to handle the case dist >= 64 here (see above). */
    Assert(dist < 64);
#if !defined(RYU_32_BIT_PLATFORM)
    Assert(dist > 0);
    return (hi << (64 - dist)) | (lo >> dist);
#else
    /* Avoid a 64-bit shift by taking advantage of the range of shift values. */
    Assert(dist >= 32);
    return (hi << (64 - dist)) | ((uint32) (lo >> 32) >> (dist - 32));
#endif
}
 
#endif                          /* // defined(HAS_64_BIT_INTRINSICS) */
 
#ifdef RYU_32_BIT_PLATFORM
 
/*  Returns the high 64 bits of the 128-bit product of a and b. */
static inline uint64
umulh(const uint64 a, const uint64 b)
{
    /*
     * Reuse the umul128 implementation. Optimizers will likely eliminate the
     * instructions used to compute the low part of the product.
     */
    uint64      hi;
 
    umul128(a, b, &hi);
    return hi;
}
 
/*----
 *  On 32-bit platforms, compilers typically generate calls to library
 *  functions for 64-bit divisions, even if the divisor is a constant.
 *
 *  E.g.:
 *  https://bugs.llvm.org/show_bug.cgi?id=37932
 *  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=17958
 *  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37443
 *
 *  The functions here perform division-by-constant using multiplications
 *  in the same way as 64-bit compilers would do.
 *
 *  NB:
 *  The multipliers and shift values are the ones generated by clang x64
 *  for expressions like x/5, x/10, etc.
 *----
 */
 
static inline uint64
div5(const uint64 x)
{
    return umulh(x, UINT64CONST(0xCCCCCCCCCCCCCCCD)) >> 2;
}
 
static inline uint64
div10(const uint64 x)
{
    return umulh(x, UINT64CONST(0xCCCCCCCCCCCCCCCD)) >> 3;
}
 
static inline uint64
div100(const uint64 x)
{
    return umulh(x >> 2, UINT64CONST(0x28F5C28F5C28F5C3)) >> 2;
}
 
static inline uint64
div1e8(const uint64 x)
{
    return umulh(x, UINT64CONST(0xABCC77118461CEFD)) >> 26;
}
 
#else                           /* RYU_32_BIT_PLATFORM */
 
static inline uint64
div5(const uint64 x)
{
    return x / 5;
}
 
static inline uint64
div10(const uint64 x)
{
    return x / 10;
}
 
static inline uint64
div100(const uint64 x)
{
    return x / 100;
}
 
static inline uint64
div1e8(const uint64 x)
{
    return x / 100000000;
}
 
#endif                          /* RYU_32_BIT_PLATFORM */
 
#endif                          /* RYU_D2S_INTRINSICS_H */