On Mon, Sep 24, 2018 at 7:15 PM Marek Olšák <mar...@gmail.com> wrote:
> This patch also handles all types, just differently. If you change the > typedefs in the header, you'll get a different type and the code is > exactly the same for all types, but that's not important (to me > anyway). > > It also supports signed division. (not important to me either, but may > be important to you) > Mine supported signed division as well though what's here might be a bit more clever. I'll have to give it some thought. > Did you figure out the algorithm by yourself or did you copy it from > somewhere? The reason I'm asking is that yours only seems to implement > the Round-Up algorithm and you said: > > "In particular, we want to have m < 2^N so that we don't have any > overflow problems. Unfortunately, this isn't always achievable." > Yes, mine is based on the round up algorithm. However, it's not the blind round-up algorithm; it's a bit smarter than that. > Let me tell you what. This patch achieves it ALWAYS. > I don't think that's true. You still have an N+1 bit multiplier, you just call it the increment bit. The saturated add, however, is a neat trick that probably lets you avoid the weirness around adding in the increment factor. I'll need to look at the web-site you linked and think about this stuff again before I can verify it. > This patch implements 2 algorithms for unsigned division: Round-Up and > Round-Down. The paper I linked shows that the Round Down algorithm > generates better code for some divisors than the Round Up algorithm, > because the multiplier always fits into 32 bits. The most operations > you'll ever need are: 2 shifts, 32-bit saturated ADD and UMUL_HI. > > Marek > > On Mon, Sep 24, 2018 at 7:41 PM, Marek Olšák <mar...@gmail.com> wrote: > > Did you copy the code from the same author? > > > > Does your version also have an interface for dividing by a uniform > > instead of a compile time constant? > > > > 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. > > > > Marek > > > > On Mon, Sep 24, 2018 at 10:00 AM, Jason Ekstrand <ja...@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 <i...@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.ol...@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; > This is wrong for non-32-bit > >>> > + 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; > So is this. Can we at the very least pull in the unit tests from my series? --Jason > >>> > + 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@lists.freedesktop.org > >>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev >
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