[Mesa-dev] [PATCH 1/5] util: import public domain code for integer division by a constant
Ian Romanick
idr at freedesktop.org
Tue Sep 25 11:21:20 UTC 2018
On 09/25/2018 02:24 AM, Jason Ekstrand wrote:
> On Mon, Sep 24, 2018 at 6:41 PM Marek Olšák <maraeo at gmail.com
> <mailto:maraeo at gmail.com>> wrote:
>
> Did you copy the code from the same author?
>
>
> No, I read a paper and implemented it myself.
>
>
> Does your version also have an interface for dividing by a uniform
> instead of a compile time constant?
>
>
> I'm not sure what you mean by that.
His code has the ability to pass in a couple extra uniforms to optimize
things like
uniform uint x;
...
a = b / x;
It seems to only work for unsigned division.
> Note that this algorithm was originally only written for
> non-power-of-two divisors and I extended it to support 1 and
> power-of-two divisors in order to support dividing by a uniform in a
> generic way. The other two generic variants that I added are also
> important. One of them assumes no unsigned wraparounds and the other
> one assumes operands have 31 bits and the divisor is >= 2.
>
>
> Right. I can see those being useful.
>
>
> Marek
>
> On Mon, Sep 24, 2018 at 10:00 AM, Jason Ekstrand
> <jason at jlekstrand.net <mailto:jason at jlekstrand.net>> wrote:
> > Very similar.... And mine handles 8, 16, and 64-bit types. :-D
> >
> > --Jason
> >
> > On Mon, Sep 24, 2018 at 8:53 AM Ian Romanick <idr at freedesktop.org
> <mailto:idr at freedesktop.org>> wrote:
> >>
> >> I didn't look really closely at either set, but this seems really
> >> similar to something Jason sent out a week or two. Perhaps you guys
> >> could unify these?
> >>
> >> On 09/23/2018 09:57 AM, Marek Olšák wrote:
> >> > From: Marek Olšák <marek.olsak at amd.com
> <mailto:marek.olsak at amd.com>>
> >> >
> >> > Compilers can use this to generate optimal code for integer
> division
> >> > by a constant.
> >> >
> >> > Additionally, an unsigned division by a uniform that is
> constant but not
> >> > known at compile time can still be optimized by passing 2-4
> division
> >> > factors to the shader as uniforms and executing one of the
> fast_udiv*
> >> > variants. The signed division algorithm doesn't have this
> capability.
> >> > ---
> >> > src/util/Makefile.sources | 2 +
> >> > src/util/fast_idiv_by_const.c | 245
> >> > ++++++++++++++++++++++++++++++++++++++++++
> >> > src/util/fast_idiv_by_const.h | 173 +++++++++++++++++++++++++++++
> >> > src/util/meson.build | 2 +
> >> > 4 files changed, 422 insertions(+)
> >> > create mode 100644 src/util/fast_idiv_by_const.c
> >> > create mode 100644 src/util/fast_idiv_by_const.h
> >> >
> >> > diff --git a/src/util/Makefile.sources b/src/util/Makefile.sources
> >> > index b562d6c..f741b2a 100644
> >> > --- a/src/util/Makefile.sources
> >> > +++ b/src/util/Makefile.sources
> >> > @@ -3,20 +3,22 @@ MESA_UTIL_FILES := \
> >> > bitscan.h \
> >> > bitset.h \
> >> > build_id.c \
> >> > build_id.h \
> >> > crc32.c \
> >> > crc32.h \
> >> > debug.c \
> >> > debug.h \
> >> > disk_cache.c \
> >> > disk_cache.h \
> >> > + fast_idiv_by_const.c \
> >> > + fast_idiv_by_const.h \
> >> > format_r11g11b10f.h \
> >> > format_rgb9e5.h \
> >> > format_srgb.h \
> >> > futex.h \
> >> > half_float.c \
> >> > half_float.h \
> >> > hash_table.c \
> >> > hash_table.h \
> >> > list.h \
> >> > macros.h \
> >> > diff --git a/src/util/fast_idiv_by_const.c
> >> > b/src/util/fast_idiv_by_const.c
> >> > new file mode 100644
> >> > index 0000000..f247b66
> >> > --- /dev/null
> >> > +++ b/src/util/fast_idiv_by_const.c
> >> > @@ -0,0 +1,245 @@
> >> > +/*
> >> > + * Copyright © 2018 Advanced Micro Devices, Inc.
> >> > + *
> >> > + * 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
> (including the
> >> > next
> >> > + * paragraph) 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.
> >> > + */
> >> > +
> >> > +/* Imported from:
> >> > + *
> >> >
> https://raw.githubusercontent.com/ridiculousfish/libdivide/master/divide_by_constants_codegen_reference.c
> >> > + * Paper:
> >> > + *
> >> >
> http://ridiculousfish.com/files/faster_unsigned_division_by_constants.pdf
> >> > + *
> >> > + * The author, ridiculous_fish, wrote:
> >> > + *
> >> > + * ''Reference implementations of computing and using the "magic
> >> > number"
> >> > + * approach to dividing by constants, including codegen
> >> > instructions.
> >> > + * The unsigned division incorporates the "round down"
> optimization
> >> > per
> >> > + * ridiculous_fish.
> >> > + *
> >> > + * This is free and unencumbered software. Any copyright is
> >> > dedicated
> >> > + * to the Public Domain.''
> >> > + */
> >> > +
> >> > +#include "fast_idiv_by_const.h"
> >> > +#include "u_math.h"
> >> > +#include <limits.h>
> >> > +#include <assert.h>
> >> > +
> >> > +/* uint_t and sint_t can be replaced by different integer
> types and the
> >> > code
> >> > + * will work as-is. The only requirement is that sizeof(uintN) ==
> >> > sizeof(intN).
> >> > + */
> >> > +
> >> > +struct util_fast_udiv_info
> >> > +util_compute_fast_udiv_info(uint_t D, unsigned num_bits)
> >> > +{
> >> > + /* The numerator must fit in a uint_t */
> >> > + assert(num_bits > 0 && num_bits <= sizeof(uint_t) * CHAR_BIT);
> >> > + assert(D != 0);
> >> > +
> >> > + /* The eventual result */
> >> > + struct util_fast_udiv_info result;
> >> > +
> >> > + if (util_is_power_of_two_nonzero(D)) {
> >> > + unsigned div_shift = util_logbase2(D);
> >> > +
> >> > + if (div_shift) {
> >> > + /* Dividing by a power of two. */
> >> > + result.multiplier = 1 << 31;
> >> > + result.pre_shift = 0;
> >> > + result.post_shift = div_shift - 1;
> >> > + result.increment = 0;
> >> > + return result;
> >> > + } else {
> >> > + /* Dividing by 1. */
> >> > + /* Assuming: floor((num + 1) * (2^32 - 1) / 2^32) =
> num */
> >> > + result.multiplier = UINT_MAX;
> >> > + result.pre_shift = 0;
> >> > + result.post_shift = 0;
> >> > + result.increment = 1;
> >> > + return result;
> >> > + }
> >> > + }
> >> > +
> >> > + /* Bits in a uint_t */
> >> > + const unsigned UINT_BITS = sizeof(uint_t) * CHAR_BIT;
> >> > +
> >> > + /* The extra shift implicit in the difference between
> UINT_BITS and
> >> > num_bits
> >> > + */
> >> > + const unsigned extra_shift = UINT_BITS - num_bits;
> >> > +
> >> > + /* The initial power of 2 is one less than the first one
> that can
> >> > possibly
> >> > + * work.
> >> > + */
> >> > + const uint_t initial_power_of_2 = (uint_t)1 << (UINT_BITS-1);
> >> > +
> >> > + /* The remainder and quotient of our power of 2 divided by d */
> >> > + uint_t quotient = initial_power_of_2 / D;
> >> > + uint_t remainder = initial_power_of_2 % D;
> >> > +
> >> > + /* ceil(log_2 D) */
> >> > + unsigned ceil_log_2_D;
> >> > +
> >> > + /* The magic info for the variant "round down" algorithm */
> >> > + uint_t down_multiplier = 0;
> >> > + unsigned down_exponent = 0;
> >> > + int has_magic_down = 0;
> >> > +
> >> > + /* Compute ceil(log_2 D) */
> >> > + ceil_log_2_D = 0;
> >> > + uint_t tmp;
> >> > + for (tmp = D; tmp > 0; tmp >>= 1)
> >> > + ceil_log_2_D += 1;
> >> > +
> >> > +
> >> > + /* Begin a loop that increments the exponent, until we find
> a power
> >> > of 2
> >> > + * that works.
> >> > + */
> >> > + unsigned exponent;
> >> > + for (exponent = 0; ; exponent++) {
> >> > + /* Quotient and remainder is from previous exponent;
> compute it
> >> > for this
> >> > + * exponent.
> >> > + */
> >> > + if (remainder >= D - remainder) {
> >> > + /* Doubling remainder will wrap around D */
> >> > + quotient = quotient * 2 + 1;
> >> > + remainder = remainder * 2 - D;
> >> > + } else {
> >> > + /* Remainder will not wrap */
> >> > + quotient = quotient * 2;
> >> > + remainder = remainder * 2;
> >> > + }
> >> > +
> >> > + /* We're done if this exponent works for the round_up
> algorithm.
> >> > + * Note that exponent may be larger than the maximum shift
> >> > supported,
> >> > + * so the check for >= ceil_log_2_D is critical.
> >> > + */
> >> > + if ((exponent + extra_shift >= ceil_log_2_D) ||
> >> > + (D - remainder) <= ((uint_t)1 << (exponent +
> extra_shift)))
> >> > + break;
> >> > +
> >> > + /* Set magic_down if we have not set it yet and this
> exponent
> >> > works for
> >> > + * the round_down algorithm
> >> > + */
> >> > + if (!has_magic_down &&
> >> > + remainder <= ((uint_t)1 << (exponent + extra_shift))) {
> >> > + has_magic_down = 1;
> >> > + down_multiplier = quotient;
> >> > + down_exponent = exponent;
> >> > + }
> >> > + }
> >> > +
> >> > + if (exponent < ceil_log_2_D) {
> >> > + /* magic_up is efficient */
> >> > + result.multiplier = quotient + 1;
> >> > + result.pre_shift = 0;
> >> > + result.post_shift = exponent;
> >> > + result.increment = 0;
> >> > + } else if (D & 1) {
> >> > + /* Odd divisor, so use magic_down, which must have been
> set */
> >> > + assert(has_magic_down);
> >> > + result.multiplier = down_multiplier;
> >> > + result.pre_shift = 0;
> >> > + result.post_shift = down_exponent;
> >> > + result.increment = 1;
> >> > + } else {
> >> > + /* Even divisor, so use a prefix-shifted dividend */
> >> > + unsigned pre_shift = 0;
> >> > + uint_t shifted_D = D;
> >> > + while ((shifted_D & 1) == 0) {
> >> > + shifted_D >>= 1;
> >> > + pre_shift += 1;
> >> > + }
> >> > + result = util_compute_fast_udiv_info(shifted_D, num_bits -
> >> > pre_shift);
> >> > + /* expect no increment or pre_shift in this path */
> >> > + assert(result.increment == 0 && result.pre_shift == 0);
> >> > + result.pre_shift = pre_shift;
> >> > + }
> >> > + return result;
> >> > +}
> >> > +
> >> > +struct util_fast_sdiv_info
> >> > +util_compute_fast_sdiv_info(sint_t D)
> >> > +{
> >> > + /* D must not be zero. */
> >> > + assert(D != 0);
> >> > + /* The result is not correct for these divisors. */
> >> > + assert(D != 1 && D != -1);
> >> > +
> >> > + /* Our result */
> >> > + struct util_fast_sdiv_info result;
> >> > +
> >> > + /* Bits in an sint_t */
> >> > + const unsigned SINT_BITS = sizeof(sint_t) * CHAR_BIT;
> >> > +
> >> > + /* Absolute value of D (we know D is not the most negative
> value
> >> > since
> >> > + * that's a power of 2)
> >> > + */
> >> > + const uint_t abs_d = (D < 0 ? -D : D);
> >> > +
> >> > + /* The initial power of 2 is one less than the first one
> that can
> >> > possibly
> >> > + * work */
> >> > + /* "two31" in Warren */
> >> > + unsigned exponent = SINT_BITS - 1;
> >> > + const uint_t initial_power_of_2 = (uint_t)1 << exponent;
> >> > +
> >> > + /* Compute the absolute value of our "test numerator,"
> >> > + * which is the largest dividend whose remainder with d is d-1.
> >> > + * This is called anc in Warren.
> >> > + */
> >> > + const uint_t tmp = initial_power_of_2 + (D < 0);
> >> > + const uint_t abs_test_numer = tmp - 1 - tmp % abs_d;
> >> > +
> >> > + /* Initialize our quotients and remainders (q1, r1, q2, r2 in
> >> > Warren) */
> >> > + uint_t quotient1 = initial_power_of_2 / abs_test_numer;
> >> > + uint_t remainder1 = initial_power_of_2 % abs_test_numer;
> >> > + uint_t quotient2 = initial_power_of_2 / abs_d;
> >> > + uint_t remainder2 = initial_power_of_2 % abs_d;
> >> > + uint_t delta;
> >> > +
> >> > + /* Begin our loop */
> >> > + do {
> >> > + /* Update the exponent */
> >> > + exponent++;
> >> > +
> >> > + /* Update quotient1 and remainder1 */
> >> > + quotient1 *= 2;
> >> > + remainder1 *= 2;
> >> > + if (remainder1 >= abs_test_numer) {
> >> > + quotient1 += 1;
> >> > + remainder1 -= abs_test_numer;
> >> > + }
> >> > +
> >> > + /* Update quotient2 and remainder2 */
> >> > + quotient2 *= 2;
> >> > + remainder2 *= 2;
> >> > + if (remainder2 >= abs_d) {
> >> > + quotient2 += 1;
> >> > + remainder2 -= abs_d;
> >> > + }
> >> > +
> >> > + /* Keep going as long as (2**exponent) / abs_d <= delta */
> >> > + delta = abs_d - remainder2;
> >> > + } while (quotient1 < delta || (quotient1 == delta &&
> remainder1 ==
> >> > 0));
> >> > +
> >> > + result.multiplier = quotient2 + 1;
> >> > + if (D < 0) result.multiplier = -result.multiplier;
> >> > + result.shift = exponent - SINT_BITS;
> >> > + return result;
> >> > +}
> >> > diff --git a/src/util/fast_idiv_by_const.h
> >> > b/src/util/fast_idiv_by_const.h
> >> > new file mode 100644
> >> > index 0000000..e8debbf
> >> > --- /dev/null
> >> > +++ b/src/util/fast_idiv_by_const.h
> >> > @@ -0,0 +1,173 @@
> >> > +/*
> >> > + * Copyright © 2018 Advanced Micro Devices, Inc.
> >> > + *
> >> > + * 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
> (including the
> >> > next
> >> > + * paragraph) 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 FAST_IDIV_BY_CONST_H
> >> > +#define FAST_IDIV_BY_CONST_H
> >> > +
> >> > +/* Imported from:
> >> > + *
> >> >
> https://raw.githubusercontent.com/ridiculousfish/libdivide/master/divide_by_constants_codegen_reference.c
> >> > + */
> >> > +
> >> > +#include <inttypes.h>
> >> > +#include <limits.h>
> >> > +#include <assert.h>
> >> > +
> >> > +/* You can set these to different types to get different
> precision. */
> >> > +typedef int32_t sint_t;
> >> > +typedef uint32_t uint_t;
> >> > +
> >> > +/* Computes "magic info" for performing signed division by a fixed
> >> > integer D.
> >> > + * The type 'sint_t' is assumed to be defined as a signed
> integer type
> >> > large
> >> > + * enough to hold both the dividend and the divisor.
> >> > + * Here >> is arithmetic (signed) shift, and >>> is logical shift.
> >> > + *
> >> > + * To emit code for n/d, rounding towards zero, use the following
> >> > sequence:
> >> > + *
> >> > + * m = compute_signed_magic_info(D)
> >> > + * emit("result = (m.multiplier * n) >> SINT_BITS");
> >> > + * if d > 0 and m.multiplier < 0: emit("result += n")
> >> > + * if d < 0 and m.multiplier > 0: emit("result -= n")
> >> > + * if m.post_shift > 0: emit("result >>= m.shift")
> >> > + * emit("result += (result < 0)")
> >> > + *
> >> > + * The shifts by SINT_BITS may be "free" if the high half of
> the full
> >> > multiply
> >> > + * is put in a separate register.
> >> > + *
> >> > + * The final add can of course be implemented via the sign
> bit, e.g.
> >> > + * result += (result >>> (SINT_BITS - 1))
> >> > + * or
> >> > + * result -= (result >> (SINT_BITS - 1))
> >> > + *
> >> > + * This code is heavily indebted to Hacker's Delight by Henry
> Warren.
> >> > + * See http://www.hackersdelight.org/HDcode/magic.c.txt
> >> > + * Used with permission from
> >> > http://www.hackersdelight.org/permissions.htm
> >> > + */
> >> > +
> >> > +struct util_fast_sdiv_info {
> >> > + sint_t multiplier; /* the "magic number" multiplier */
> >> > + unsigned shift; /* shift for the dividend after multiplying */
> >> > +};
> >> > +
> >> > +struct util_fast_sdiv_info
> >> > +util_compute_fast_sdiv_info(sint_t D);
> >> > +
> >> > +/* Computes "magic info" for performing unsigned division by a
> fixed
> >> > positive
> >> > + * integer D. The type 'uint_t' is assumed to be defined as an
> unsigned
> >> > + * integer type large enough to hold both the dividend and the
> divisor.
> >> > + * num_bits can be set appropriately if n is known to be
> smaller than
> >> > + * the largest uint_t; if this is not known then pass
> >> > + * "(sizeof(uint_t) * CHAR_BIT)" for num_bits.
> >> > + *
> >> > + * Assume we have a hardware register of width UINT_BITS, a known
> >> > constant D
> >> > + * which is not zero and not a power of 2, and a variable n
> of width
> >> > num_bits
> >> > + * (which may be up to UINT_BITS). To emit code for n/d, use
> one of the
> >> > two
> >> > + * following sequences (here >>> refers to a logical bitshift):
> >> > + *
> >> > + * m = compute_unsigned_magic_info(D, num_bits)
> >> > + * if m.pre_shift > 0: emit("n >>>= m.pre_shift")
> >> > + * if m.increment: emit("n = saturated_increment(n)")
> >> > + * emit("result = (m.multiplier * n) >>> UINT_BITS")
> >> > + * if m.post_shift > 0: emit("result >>>= m.post_shift")
> >> > + *
> >> > + * or
> >> > + *
> >> > + * m = compute_unsigned_magic_info(D, num_bits)
> >> > + * if m.pre_shift > 0: emit("n >>>= m.pre_shift")
> >> > + * emit("result = m.multiplier * n")
> >> > + * if m.increment: emit("result = result + m.multiplier")
> >> > + * emit("result >>>= UINT_BITS")
> >> > + * if m.post_shift > 0: emit("result >>>= m.post_shift")
> >> > + *
> >> > + * The shifts by UINT_BITS may be "free" if the high half of
> the full
> >> > multiply
> >> > + * is put in a separate register.
> >> > + *
> >> > + * saturated_increment(n) means "increment n unless it would
> wrap to
> >> > 0," i.e.
> >> > + * if n == (1 << UINT_BITS)-1: result = n
> >> > + * else: result = n+1
> >> > + * A common way to implement this is with the carry bit. For
> example,
> >> > on x86:
> >> > + * add 1
> >> > + * sbb 0
> >> > + *
> >> > + * Some invariants:
> >> > + * 1: At least one of pre_shift and increment is zero
> >> > + * 2: multiplier is never zero
> >> > + *
> >> > + * This code incorporates the "round down" optimization per
> >> > ridiculous_fish.
> >> > + */
> >> > +
> >> > +struct util_fast_udiv_info {
> >> > + uint_t multiplier; /* the "magic number" multiplier */
> >> > + unsigned pre_shift; /* shift for the dividend before
> multiplying */
> >> > + unsigned post_shift; /* shift for the dividend after
> multiplying */
> >> > + int increment; /* 0 or 1; if set then increment the
> numerator, using
> >> > one of
> >> > + the two strategies */
> >> > +};
> >> > +
> >> > +struct util_fast_udiv_info
> >> > +util_compute_fast_udiv_info(uint_t D, unsigned num_bits);
> >> > +
> >> > +/* Below are possible options for dividing by a uniform in a
> shader
> >> > where
> >> > + * the divisor is constant but not known at compile time.
> >> > + */
> >> > +
> >> > +/* Full version. */
> >> > +static inline unsigned
> >> > +fast_udiv(unsigned n, struct util_fast_udiv_info info)
> >> > +{
> >> > + n = n >> info.pre_shift;
> >> > + /* For non-power-of-two divisors, use a 32-bit ADD that
> clamps to
> >> > UINT_MAX. */
> >> > + n = (((uint64_t)n + info.increment) * info.multiplier) >> 32;
> >> > + n = n >> info.post_shift;
> >> > + return n;
> >> > +}
> >> > +
> >> > +/* A little more efficient version if n != UINT_MAX, i.e. no
> unsigned
> >> > + * wraparound in the computation.
> >> > + */
> >> > +static inline unsigned
> >> > +fast_udiv_nuw(unsigned n, struct util_fast_udiv_info info)
> >> > +{
> >> > + assert(n != UINT_MAX);
> >> > + n = n >> info.pre_shift;
> >> > + n = n + info.increment;
> >> > + n = ((uint64_t)n * info.multiplier) >> 32;
> >> > + n = n >> info.post_shift;
> >> > + return n;
> >> > +}
> >> > +
> >> > +/* Even faster version but both operands must be 31-bit unsigned
> >> > integers
> >> > + * and the divisor must be greater than 1.
> >> > + *
> >> > + * info must be computed with num_bits == 31.
> >> > + */
> >> > +static inline unsigned
> >> > +fast_udiv_u31_d_not_one(unsigned n, struct util_fast_udiv_info
> info)
> >> > +{
> >> > + assert(info.pre_shift == 0);
> >> > + assert(info.increment == 0);
> >> > + n = ((uint64_t)n * info.multiplier) >> 32;
> >> > + n = n >> info.post_shift;
> >> > + return n;
> >> > +}
> >> > +
> >> > +#endif
> >> > diff --git a/src/util/meson.build b/src/util/meson.build
> >> > index 027bc5b..ebaeb47 100644
> >> > --- a/src/util/meson.build
> >> > +++ b/src/util/meson.build
> >> > @@ -27,20 +27,22 @@ files_mesa_util = files(
> >> > 'bitscan.h',
> >> > 'bitset.h',
> >> > 'build_id.c',
> >> > 'build_id.h',
> >> > 'crc32.c',
> >> > 'crc32.h',
> >> > 'debug.c',
> >> > 'debug.h',
> >> > 'disk_cache.c',
> >> > 'disk_cache.h',
> >> > + 'fast_idiv_by_const.c',
> >> > + 'fast_idiv_by_const.h',
> >> > 'format_r11g11b10f.h',
> >> > 'format_rgb9e5.h',
> >> > 'format_srgb.h',
> >> > 'futex.h',
> >> > 'half_float.c',
> >> > 'half_float.h',
> >> > 'hash_table.c',
> >> > 'hash_table.h',
> >> > 'list.h',
> >> > 'macros.h',
> >> >
> >>
> >> _______________________________________________
> >> mesa-dev mailing list
> >> mesa-dev at lists.freedesktop.org
> <mailto:mesa-dev at lists.freedesktop.org>
> >> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>
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