src/gallium/auxiliary/gallivm/lp_bld_conv.c

   1 /**************************************************************************
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   3  * Copyright 2009 VMware, Inc.
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  27
  28
  29 /**
  30  * @file
  31  * Helper functions for type conversions.
  32  *
  33  * We want to use the fastest type for a given computation whenever feasible.
  34  * The other side of this is that we need to be able convert between several
  35  * types accurately and efficiently.
  36  *
  37  * Conversion between types of different bit width is quite complex since a
  38  *
  39  * To remember there are a few invariants in type conversions:
  40  *
  41  * - register width must remain constant:
  42  *
  43  *     src_type.width * src_type.length == dst_type.width * dst_type.length
  44  *
  45  * - total number of elements must remain constant:
  46  *
  47  *     src_type.length * num_srcs == dst_type.length * num_dsts
  48  *
  49  * It is not always possible to do the conversion both accurately and
  50  * efficiently, usually due to lack of adequate machine instructions. In these
  51  * cases it is important not to cut shortcuts here and sacrifice accuracy, as
  52  * there this functions can be used anywhere. In the future we might have a
  53  * precision parameter which can gauge the accuracy vs efficiency compromise,
  54  * but for now if the data conversion between two stages happens to be the
  55  * bottleneck, then most likely should just avoid converting at all and run
  56  * both stages with the same type.
  57  *
  58  * Make sure to run lp_test_conv unit test after any change to this file.
  59  *
  60  * @author Jose Fonseca <jfonseca@vmware.com>
  61  */
  62
  63
  64 #include "util/u_debug.h"
  65 #include "util/u_math.h"
  66 #include "util/u_cpu_detect.h"
  67
  68 #include "lp_bld_type.h"
  69 #include "lp_bld_const.h"
  70 #include "lp_bld_arit.h"
  71 #include "lp_bld_pack.h"
  72 #include "lp_bld_conv.h"
  73
  74
  75 /**
  76  * Special case for converting clamped IEEE-754 floats to unsigned norms.
  77  *
  78  * The mathematical voodoo below may seem excessive but it is actually
  79  * paramount we do it this way for several reasons. First, there is no single
  80  * precision FP to unsigned integer conversion Intel SSE instruction. Second,
  81  * secondly, even if there was, since the FP's mantissa takes only a fraction
  82  * of register bits the typically scale and cast approach would require double
  83  * precision for accurate results, and therefore half the throughput
  84  *
  85  * Although the result values can be scaled to an arbitrary bit width specified
  86  * by dst_width, the actual result type will have the same width.
  87  *
  88  * Ex: src = { float, float, float, float }
  89  * return { i32, i32, i32, i32 } where each value is in [0, 2^dst_width-1].
  90  */
  91 LLVMValueRef
  92 lp_build_clamped_float_to_unsigned_norm(struct gallivm_state *gallivm,
  93                                         struct lp_type src_type,
  94                                         unsigned dst_width,
  95                                         LLVMValueRef src)
  96 {
  97    LLVMBuilderRef builder = gallivm->builder;
  98    LLVMTypeRef int_vec_type = lp_build_int_vec_type(gallivm, src_type);
  99    LLVMValueRef res;
 100    unsigned mantissa;
 101
 102    assert(src_type.floating);
 103    assert(dst_width <= src_type.width);
 104    src_type.sign = FALSE;
 105
 106    mantissa = lp_mantissa(src_type);
 107
 108    if (dst_width <= mantissa) {
 109       /*
 110        * Apply magic coefficients that will make the desired result to appear
 111        * in the lowest significant bits of the mantissa, with correct rounding.
 112        *
 113        * This only works if the destination width fits in the mantissa.
 114        */
 115
 116       unsigned long long ubound;
 117       unsigned long long mask;
 118       double scale;
 119       double bias;
 120
 121       ubound = (1ULL << dst_width);
 122       mask = ubound - 1;
 123       scale = (double)mask/ubound;
 124       bias = (double)(1ULL << (mantissa - dst_width));
 125
 126       res = LLVMBuildFMul(builder, src, lp_build_const_vec(gallivm, src_type, scale), "");
 127       res = LLVMBuildFAdd(builder, res, lp_build_const_vec(gallivm, src_type, bias), "");
 128       res = LLVMBuildBitCast(builder, res, int_vec_type, "");
 129       res = LLVMBuildAnd(builder, res,
 130                          lp_build_const_int_vec(gallivm, src_type, mask), "");
 131    }
 132    else if (dst_width == (mantissa + 1)) {
 133       /*
 134        * The destination width matches exactly what can be represented in
 135        * floating point (i.e., mantissa + 1 bits). So do a straight
 136        * multiplication followed by casting. No further rounding is necessary.
 137        */
 138
 139       double scale;
 140
 141       scale = (double)((1ULL << dst_width) - 1);
 142
 143       res = LLVMBuildFMul(builder, src,
 144                           lp_build_const_vec(gallivm, src_type, scale), "");
 145       res = LLVMBuildFPToSI(builder, res, int_vec_type, "");
 146    }
 147    else {
 148       /*
 149        * The destination exceeds what can be represented in the floating point.
 150        * So multiply by the largest power two we get away with, and when
 151        * subtract the most significant bit to rescale to normalized values.
 152        *
 153        * The largest power of two factor we can get away is
 154        * (1 << (src_type.width - 1)), because we need to use signed . In theory it
 155        * should be (1 << (src_type.width - 2)), but IEEE 754 rules states
 156        * INT_MIN should be returned in FPToSI, which is the correct result for
 157        * values near 1.0!
 158        *
 159        * This means we get (src_type.width - 1) correct bits for values near 0.0,
 160        * and (mantissa + 1) correct bits for values near 1.0. Equally or more
 161        * important, we also get exact results for 0.0 and 1.0.
 162        */
 163
 164       unsigned n = MIN2(src_type.width - 1, dst_width);
 165
 166       double scale = (double)(1ULL << n);
 167       unsigned lshift = dst_width - n;
 168       unsigned rshift = n;
 169       LLVMValueRef lshifted;
 170       LLVMValueRef rshifted;
 171
 172       res = LLVMBuildFMul(builder, src,
 173                           lp_build_const_vec(gallivm, src_type, scale), "");
 174       res = LLVMBuildFPToSI(builder, res, int_vec_type, "");
 175
 176       /*
 177        * Align the most significant bit to its final place.
 178        *
 179        * This will cause 1.0 to overflow to 0, but the later adjustment will
 180        * get it right.
 181        */
 182       if (lshift) {
 183          lshifted = LLVMBuildShl(builder, res,
 184                                  lp_build_const_int_vec(gallivm, src_type,
 185                                                         lshift), "");
 186       } else {
 187          lshifted = res;
 188       }
 189
 190       /*
 191        * Align the most significant bit to the right.
 192        */
 193       rshifted =  LLVMBuildAShr(builder, res,
 194                                 lp_build_const_int_vec(gallivm, src_type, rshift),
 195                                 "");
 196
 197       /*
 198        * Subtract the MSB to the LSB, therefore re-scaling from
 199        * (1 << dst_width) to ((1 << dst_width) - 1).
 200        */
 201
 202       res = LLVMBuildSub(builder, lshifted, rshifted, "");
 203    }
 204
 205    return res;
 206 }
 207
 208
 209 /**
 210  * Inverse of lp_build_clamped_float_to_unsigned_norm above.
 211  * Ex: src = { i32, i32, i32, i32 } with values in range [0, 2^src_width-1]
 212  * return {float, float, float, float} with values in range [0, 1].
 213  */
 214 LLVMValueRef
 215 lp_build_unsigned_norm_to_float(struct gallivm_state *gallivm,
 216                                 unsigned src_width,
 217                                 struct lp_type dst_type,
 218                                 LLVMValueRef src)
 219 {
 220    LLVMBuilderRef builder = gallivm->builder;
 221    LLVMTypeRef vec_type = lp_build_vec_type(gallivm, dst_type);
 222    LLVMTypeRef int_vec_type = lp_build_int_vec_type(gallivm, dst_type);
 223    LLVMValueRef bias_;
 224    LLVMValueRef res;
 225    unsigned mantissa;
 226    unsigned n;
 227    unsigned long long ubound;
 228    unsigned long long mask;
 229    double scale;
 230    double bias;
 231
 232    assert(dst_type.floating);
 233
 234    mantissa = lp_mantissa(dst_type);
 235
 236    if (src_width <= (mantissa + 1)) {
 237       /*
 238        * The source width matches fits what can be represented in floating
 239        * point (i.e., mantissa + 1 bits). So do a straight multiplication
 240        * followed by casting. No further rounding is necessary.
 241        */
 242
 243       scale = 1.0/(double)((1ULL << src_width) - 1);
 244       res = LLVMBuildSIToFP(builder, src, vec_type, "");
 245       res = LLVMBuildFMul(builder, res,
 246                           lp_build_const_vec(gallivm, dst_type, scale), "");
 247       return res;
 248    }
 249    else {
 250       /*
 251        * The source width exceeds what can be represented in floating
 252        * point. So truncate the incoming values.
 253        */
 254
 255       n = MIN2(mantissa, src_width);
 256
 257       ubound = ((unsigned long long)1 << n);
 258       mask = ubound - 1;
 259       scale = (double)ubound/mask;
 260       bias = (double)((unsigned long long)1 << (mantissa - n));
 261
 262       res = src;
 263
 264       if (src_width > mantissa) {
 265          int shift = src_width - mantissa;
 266          res = LLVMBuildLShr(builder, res,
 267                              lp_build_const_int_vec(gallivm, dst_type, shift), "");
 268       }
 269
 270       bias_ = lp_build_const_vec(gallivm, dst_type, bias);
 271
 272       res = LLVMBuildOr(builder,
 273                         res,
 274                         LLVMBuildBitCast(builder, bias_, int_vec_type, ""), "");
 275
 276       res = LLVMBuildBitCast(builder, res, vec_type, "");
 277
 278       res = LLVMBuildFSub(builder, res, bias_, "");
 279       res = LLVMBuildFMul(builder, res, lp_build_const_vec(gallivm, dst_type, scale), "");
 280    }
 281
 282    return res;
 283 }
 284
 285
 286 /**
 287  * Generic type conversion.
 288  *
 289  * TODO: Take a precision argument, or even better, add a new precision member
 290  * to the lp_type union.
 291  */
 292 void
 293 lp_build_conv(struct gallivm_state *gallivm,
 294               struct lp_type src_type,
 295               struct lp_type dst_type,
 296               const LLVMValueRef *src, unsigned num_srcs,
 297               LLVMValueRef *dst, unsigned num_dsts)
 298 {
 299    LLVMBuilderRef builder = gallivm->builder;
 300    struct lp_type tmp_type;
 301    LLVMValueRef tmp[LP_MAX_VECTOR_LENGTH];
 302    unsigned num_tmps;
 303    unsigned i;
 304
 305    /* We must not loose or gain channels. Only precision */
 306    assert(src_type.length * num_srcs == dst_type.length * num_dsts);
 307
 308    assert(src_type.length <= LP_MAX_VECTOR_LENGTH);
 309    assert(dst_type.length <= LP_MAX_VECTOR_LENGTH);
 310    assert(num_srcs <= LP_MAX_VECTOR_LENGTH);
 311    assert(num_dsts <= LP_MAX_VECTOR_LENGTH);
 312
 313    tmp_type = src_type;
 314    for(i = 0; i < num_srcs; ++i) {
 315       assert(lp_check_value(src_type, src[i]));
 316       tmp[i] = src[i];
 317    }
 318    num_tmps = num_srcs;
 319
 320
 321    /* Special case 4x4f --> 1x16ub
 322     */
 323    if (src_type.floating == 1 &&
 324        src_type.fixed    == 0 &&
 325        src_type.sign     == 1 &&
 326        src_type.norm     == 0 &&
 327        src_type.width    == 32 &&
 328        src_type.length   == 4 &&
 329
 330        dst_type.floating == 0 &&
 331        dst_type.fixed    == 0 &&
 332        dst_type.sign     == 0 &&
 333        dst_type.norm     == 1 &&
 334        dst_type.width    == 8 &&
 335        dst_type.length   == 16 &&
 336
 337        util_cpu_caps.has_sse2)
 338    {
 339       int i;
 340
 341       for (i = 0; i < num_dsts; i++, src += 4) {
 342          struct lp_type int16_type = dst_type;
 343          struct lp_type int32_type = dst_type;
 344          LLVMValueRef lo, hi;
 345          LLVMValueRef src_int0;
 346          LLVMValueRef src_int1;
 347          LLVMValueRef src_int2;
 348          LLVMValueRef src_int3;
 349          LLVMTypeRef int32_vec_type;
 350          LLVMTypeRef src_vec_type;
 351          LLVMValueRef const_255f;
 352          LLVMValueRef a, b, c, d;
 353
 354          int16_type.width *= 2;
 355          int16_type.length /= 2;
 356          int16_type.sign = 1;
 357
 358          int32_type.width *= 4;
 359          int32_type.length /= 4;
 360          int32_type.sign = 1;
 361
 362          src_vec_type   = lp_build_vec_type(gallivm, src_type);
 363          int32_vec_type = lp_build_vec_type(gallivm, int32_type);
 364
 365          const_255f = lp_build_const_vec(gallivm, src_type, 255.0f);
 366
 367          a = LLVMBuildFMul(builder, src[0], const_255f, "");
 368          b = LLVMBuildFMul(builder, src[1], const_255f, "");
 369          c = LLVMBuildFMul(builder, src[2], const_255f, "");
 370          d = LLVMBuildFMul(builder, src[3], const_255f, "");
 371
 372          {
 373             struct lp_build_context bld;
 374
 375             bld.gallivm = gallivm;
 376             bld.type = src_type;
 377             bld.vec_type = src_vec_type;
 378             bld.int_elem_type = lp_build_elem_type(gallivm, int32_type);
 379             bld.int_vec_type = int32_vec_type;
 380             bld.undef = lp_build_undef(gallivm, src_type);
 381             bld.zero = lp_build_zero(gallivm, src_type);
 382             bld.one = lp_build_one(gallivm, src_type);
 383
 384             src_int0 = lp_build_iround(&bld, a);
 385             src_int1 = lp_build_iround(&bld, b);
 386             src_int2 = lp_build_iround(&bld, c);
 387             src_int3 = lp_build_iround(&bld, d);
 388          }
 389          /* relying on clamping behavior of sse2 intrinsics here */
 390          lo = lp_build_pack2(gallivm, int32_type, int16_type, src_int0, src_int1);
 391          hi = lp_build_pack2(gallivm, int32_type, int16_type, src_int2, src_int3);
 392          dst[i] = lp_build_pack2(gallivm, int16_type, dst_type, lo, hi);
 393       }
 394       return;
 395    }
 396
 397    /*
 398     * Clamp if necessary
 399     */
 400
 401    if(memcmp(&src_type, &dst_type, sizeof src_type) != 0) {
 402       struct lp_build_context bld;
 403       double src_min = lp_const_min(src_type);
 404       double dst_min = lp_const_min(dst_type);
 405       double src_max = lp_const_max(src_type);
 406       double dst_max = lp_const_max(dst_type);
 407       LLVMValueRef thres;
 408
 409       lp_build_context_init(&bld, gallivm, tmp_type);
 410
 411       if(src_min < dst_min) {
 412          if(dst_min == 0.0)
 413             thres = bld.zero;
 414          else
 415             thres = lp_build_const_vec(gallivm, src_type, dst_min);
 416          for(i = 0; i < num_tmps; ++i)
 417             tmp[i] = lp_build_max(&bld, tmp[i], thres);
 418       }
 419
 420       if(src_max > dst_max) {
 421          if(dst_max == 1.0)
 422             thres = bld.one;
 423          else
 424             thres = lp_build_const_vec(gallivm, src_type, dst_max);
 425          for(i = 0; i < num_tmps; ++i)
 426             tmp[i] = lp_build_min(&bld, tmp[i], thres);
 427       }
 428    }
 429
 430    /*
 431     * Scale to the narrowest range
 432     */
 433
 434    if(dst_type.floating) {
 435       /* Nothing to do */
 436    }
 437    else if(tmp_type.floating) {
 438       if(!dst_type.fixed && !dst_type.sign && dst_type.norm) {
 439          for(i = 0; i < num_tmps; ++i) {
 440             tmp[i] = lp_build_clamped_float_to_unsigned_norm(gallivm,
 441                                                              tmp_type,
 442                                                              dst_type.width,
 443                                                              tmp[i]);
 444          }
 445          tmp_type.floating = FALSE;
 446       }
 447       else {
 448          double dst_scale = lp_const_scale(dst_type);
 449          LLVMTypeRef tmp_vec_type;
 450
 451          if (dst_scale != 1.0) {
 452             LLVMValueRef scale = lp_build_const_vec(gallivm, tmp_type, dst_scale);
 453             for(i = 0; i < num_tmps; ++i)
 454                tmp[i] = LLVMBuildFMul(builder, tmp[i], scale, "");
 455          }
 456
 457          /* Use an equally sized integer for intermediate computations */
 458          tmp_type.floating = FALSE;
 459          tmp_vec_type = lp_build_vec_type(gallivm, tmp_type);
 460          for(i = 0; i < num_tmps; ++i) {
 461 #if 0
 462             if(dst_type.sign)
 463                tmp[i] = LLVMBuildFPToSI(builder, tmp[i], tmp_vec_type, "");
 464             else
 465                tmp[i] = LLVMBuildFPToUI(builder, tmp[i], tmp_vec_type, "");
 466 #else
 467            /* FIXME: there is no SSE counterpart for LLVMBuildFPToUI */
 468             tmp[i] = LLVMBuildFPToSI(builder, tmp[i], tmp_vec_type, "");
 469 #endif
 470          }
 471       }
 472    }
 473    else {
 474       unsigned src_shift = lp_const_shift(src_type);
 475       unsigned dst_shift = lp_const_shift(dst_type);
 476
 477       /* FIXME: compensate different offsets too */
 478       if(src_shift > dst_shift) {
 479          LLVMValueRef shift = lp_build_const_int_vec(gallivm, tmp_type,
 480                                                      src_shift - dst_shift);
 481          for(i = 0; i < num_tmps; ++i)
 482             if(src_type.sign)
 483                tmp[i] = LLVMBuildAShr(builder, tmp[i], shift, "");
 484             else
 485                tmp[i] = LLVMBuildLShr(builder, tmp[i], shift, "");
 486       }
 487    }
 488
 489    /*
 490     * Truncate or expand bit width
 491     *
 492     * No data conversion should happen here, although the sign bits are
 493     * crucial to avoid bad clamping.
 494     */
 495
 496    {
 497       struct lp_type new_type;
 498
 499       new_type = tmp_type;
 500       new_type.sign   = dst_type.sign;
 501       new_type.width  = dst_type.width;
 502       new_type.length = dst_type.length;
 503
 504       lp_build_resize(gallivm, tmp_type, new_type, tmp, num_srcs, tmp, num_dsts);
 505
 506       tmp_type = new_type;
 507       num_tmps = num_dsts;
 508    }
 509
 510    /*
 511     * Scale to the widest range
 512     */
 513
 514    if(src_type.floating) {
 515       /* Nothing to do */
 516    }
 517    else if(!src_type.floating && dst_type.floating) {
 518       if(!src_type.fixed && !src_type.sign && src_type.norm) {
 519          for(i = 0; i < num_tmps; ++i) {
 520             tmp[i] = lp_build_unsigned_norm_to_float(gallivm,
 521                                                      src_type.width,
 522                                                      dst_type,
 523                                                      tmp[i]);
 524          }
 525          tmp_type.floating = TRUE;
 526       }
 527       else {
 528          double src_scale = lp_const_scale(src_type);
 529          LLVMTypeRef tmp_vec_type;
 530
 531          /* Use an equally sized integer for intermediate computations */
 532          tmp_type.floating = TRUE;
 533          tmp_type.sign = TRUE;
 534          tmp_vec_type = lp_build_vec_type(gallivm, tmp_type);
 535          for(i = 0; i < num_tmps; ++i) {
 536 #if 0
 537             if(dst_type.sign)
 538                tmp[i] = LLVMBuildSIToFP(builder, tmp[i], tmp_vec_type, "");
 539             else
 540                tmp[i] = LLVMBuildUIToFP(builder, tmp[i], tmp_vec_type, "");
 541 #else
 542             /* FIXME: there is no SSE counterpart for LLVMBuildUIToFP */
 543             tmp[i] = LLVMBuildSIToFP(builder, tmp[i], tmp_vec_type, "");
 544 #endif
 545           }
 546
 547           if (src_scale != 1.0) {
 548              LLVMValueRef scale = lp_build_const_vec(gallivm, tmp_type, 1.0/src_scale);
 549              for(i = 0; i < num_tmps; ++i)
 550                 tmp[i] = LLVMBuildFMul(builder, tmp[i], scale, "");
 551           }
 552       }
 553     }
 554     else {
 555        unsigned src_shift = lp_const_shift(src_type);
 556        unsigned dst_shift = lp_const_shift(dst_type);
 557
 558        /* FIXME: compensate different offsets too */
 559        if(src_shift < dst_shift) {
 560           LLVMValueRef shift = lp_build_const_int_vec(gallivm, tmp_type, dst_shift - src_shift);
 561           for(i = 0; i < num_tmps; ++i)
 562              tmp[i] = LLVMBuildShl(builder, tmp[i], shift, "");
 563        }
 564     }
 565
 566    for(i = 0; i < num_dsts; ++i) {
 567       dst[i] = tmp[i];
 568       assert(lp_check_value(dst_type, dst[i]));
 569    }
 570 }
 571
 572
 573 /**
 574  * Bit mask conversion.
 575  *
 576  * This will convert the integer masks that match the given types.
 577  *
 578  * The mask values should 0 or -1, i.e., all bits either set to zero or one.
 579  * Any other value will likely cause in unpredictable results.
 580  *
 581  * This is basically a very trimmed down version of lp_build_conv.
 582  */
 583 void
 584 lp_build_conv_mask(struct gallivm_state *gallivm,
 585                    struct lp_type src_type,
 586                    struct lp_type dst_type,
 587                    const LLVMValueRef *src, unsigned num_srcs,
 588                    LLVMValueRef *dst, unsigned num_dsts)
 589 {
 590    /* Register width must remain constant */
 591    assert(src_type.width * src_type.length == dst_type.width * dst_type.length);
 592
 593    /* We must not loose or gain channels. Only precision */
 594    assert(src_type.length * num_srcs == dst_type.length * num_dsts);
 595
 596    /*
 597     * Drop
 598     *
 599     * We assume all values are 0 or -1
 600     */
 601
 602    src_type.floating = FALSE;
 603    src_type.fixed = FALSE;
 604    src_type.sign = TRUE;
 605    src_type.norm = FALSE;
 606
 607    dst_type.floating = FALSE;
 608    dst_type.fixed = FALSE;
 609    dst_type.sign = TRUE;
 610    dst_type.norm = FALSE;
 611
 612    /*
 613     * Truncate or expand bit width
 614     */
 615
 616    if(src_type.width > dst_type.width) {
 617       assert(num_dsts == 1);
 618       dst[0] = lp_build_pack(gallivm, src_type, dst_type, TRUE, src, num_srcs);
 619    }
 620    else if(src_type.width < dst_type.width) {
 621       assert(num_srcs == 1);
 622       lp_build_unpack(gallivm, src_type, dst_type, src[0], dst, num_dsts);
 623    }
 624    else {
 625       assert(num_srcs == num_dsts);
 626       memcpy(dst, src, num_dsts * sizeof *dst);
 627    }
 628 }