src/gallium/auxiliary/util/u_format_pack.py

   1 #!/usr/bin/env python
   2
   3 '''
   4 /**************************************************************************
   5  *
   6  * Copyright 2009-2010 VMware, Inc.
   7  * All Rights Reserved.
   8  *
   9  * Permission is hereby granted, free of charge, to any person obtaining a
  10  * copy of this software and associated documentation files (the
  11  * "Software"), to deal in the Software without restriction, including
  12  * without limitation the rights to use, copy, modify, merge, publish,
  13  * distribute, sub license, and/or sell copies of the Software, and to
  14  * permit persons to whom the Software is furnished to do so, subject to
  15  * the following conditions:
  16  *
  17  * The above copyright notice and this permission notice (including the
  18  * next paragraph) shall be included in all copies or substantial portions
  19  * of the Software.
  20  *
  21  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  22  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  23  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
  24  * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
  25  * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  26  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  27  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  28  *
  29  **************************************************************************/
  30
  31 /**
  32  * @file
  33  * Pixel format packing and unpacking functions.
  34  *
  35  * @author Jose Fonseca <jfonseca@vmware.com>
  36  */
  37 '''
  38
  39
  40 import sys
  41 import math
  42
  43 from u_format_parse import *
  44
  45
  46 def generate_format_type(format):
  47     '''Generate a structure that describes the format.'''
  48
  49     assert format.layout == PLAIN
  50
  51     print 'union util_format_%s {' % format.short_name()
  52
  53     if format.block_size() in (8, 16, 32, 64):
  54         print '   uint%u_t value;' % (format.block_size(),)
  55
  56     use_bitfields = False
  57     for channel in format.channels:
  58         if channel.size % 8 or not is_pot(channel.size):
  59             use_bitfields = True
  60
  61     print '   struct {'
  62     for channel in format.channels:
  63         if use_bitfields:
  64             if channel.type == VOID:
  65                 if channel.size:
  66                     print '      unsigned %s:%u;' % (channel.name, channel.size)
  67             elif channel.type == UNSIGNED:
  68                 print '      unsigned %s:%u;' % (channel.name, channel.size)
  69             elif channel.type in (SIGNED, FIXED):
  70                 print '      int %s:%u;' % (channel.name, channel.size)
  71             elif channel.type == FLOAT:
  72                 if channel.size == 64:
  73                     print '      double %s;' % (channel.name)
  74                 elif channel.size == 32:
  75                     print '      float %s;' % (channel.name)
  76                 else:
  77                     print '      unsigned %s:%u;' % (channel.name, channel.size)
  78             else:
  79                 assert 0
  80         else:
  81             assert channel.size % 8 == 0 and is_pot(channel.size)
  82             if channel.type == VOID:
  83                 if channel.size:
  84                     print '      uint%u_t %s;' % (channel.size, channel.name)
  85             elif channel.type == UNSIGNED:
  86                 print '      uint%u_t %s;' % (channel.size, channel.name)
  87             elif channel.type in (SIGNED, FIXED):
  88                 print '      int%u_t %s;' % (channel.size, channel.name)
  89             elif channel.type == FLOAT:
  90                 if channel.size == 64:
  91                     print '      double %s;' % (channel.name)
  92                 elif channel.size == 32:
  93                     print '      float %s;' % (channel.name)
  94                 elif channel.size == 16:
  95                     print '      uint16_t %s;' % (channel.name)
  96                 else:
  97                     assert 0
  98             else:
  99                 assert 0
 100     print '   } chan;'
 101     print '};'
 102     print
 103
 104
 105 def bswap_format(format):
 106     '''Generate a structure that describes the format.'''
 107
 108     if format.is_bitmask() and not format.is_array() and format.block_size() > 8:
 109         print '#ifdef PIPE_ARCH_BIG_ENDIAN'
 110         print '   pixel.value = util_bswap%u(pixel.value);' % format.block_size()
 111         print '#endif'
 112
 113
 114 def is_format_supported(format):
 115     '''Determines whether we actually have the plumbing necessary to generate the
 116     to read/write to/from this format.'''
 117
 118     # FIXME: Ideally we would support any format combination here.
 119
 120     if format.layout != PLAIN:
 121         return False
 122
 123     for i in range(4):
 124         channel = format.channels[i]
 125         if channel.type not in (VOID, UNSIGNED, SIGNED, FLOAT, FIXED):
 126             return False
 127         if channel.type == FLOAT and channel.size not in (16, 32, 64):
 128             return False
 129
 130     return True
 131
 132
 133 def native_type(format):
 134     '''Get the native appropriate for a format.'''
 135
 136     if format.layout == PLAIN:
 137         if not format.is_array():
 138             # For arithmetic pixel formats return the integer type that matches the whole pixel
 139             return 'uint%u_t' % format.block_size()
 140         else:
 141             # For array pixel formats return the integer type that matches the color channel
 142             channel = format.channels[0]
 143             if channel.type in (UNSIGNED, VOID):
 144                 return 'uint%u_t' % channel.size
 145             elif channel.type in (SIGNED, FIXED):
 146                 return 'int%u_t' % channel.size
 147             elif channel.type == FLOAT:
 148                 if channel.size == 16:
 149                     return 'uint16_t'
 150                 elif channel.size == 32:
 151                     return 'float'
 152                 elif channel.size == 64:
 153                     return 'double'
 154                 else:
 155                     assert False
 156             else:
 157                 assert False
 158     else:
 159         assert False
 160
 161
 162 def intermediate_native_type(bits, sign):
 163     '''Find a native type adequate to hold intermediate results of the request bit size.'''
 164
 165     bytes = 4 # don't use anything smaller than 32bits
 166     while bytes * 8 < bits:
 167         bytes *= 2
 168     bits = bytes*8
 169
 170     if sign:
 171         return 'int%u_t' % bits
 172     else:
 173         return 'uint%u_t' % bits
 174
 175
 176 def get_one_shift(type):
 177     '''Get the number of the bit that matches unity for this type.'''
 178     if type.type == 'FLOAT':
 179         assert False
 180     if not type.norm:
 181         return 0
 182     if type.type == UNSIGNED:
 183         return type.size
 184     if type.type == SIGNED:
 185         return type.size - 1
 186     if type.type == FIXED:
 187         return type.size / 2
 188     assert False
 189
 190
 191 def value_to_native(type, value):
 192     '''Get the value of unity for this type.'''
 193     if type.type == FLOAT:
 194         return value
 195     if type.type == FIXED:
 196         return int(value * (1 << (type.size/2)))
 197     if not type.norm:
 198         return int(value)
 199     if type.type == UNSIGNED:
 200         return int(value * ((1 << type.size) - 1))
 201     if type.type == SIGNED:
 202         return int(value * ((1 << (type.size - 1)) - 1))
 203     assert False
 204
 205
 206 def native_to_constant(type, value):
 207     '''Get the value of unity for this type.'''
 208     if type.type == FLOAT:
 209         if type.size <= 32:
 210             return "%ff" % value
 211         else:
 212             return "%ff" % value
 213     else:
 214         return str(int(value))
 215
 216
 217 def get_one(type):
 218     '''Get the value of unity for this type.'''
 219     return value_to_native(type, 1)
 220
 221
 222 def clamp_expr(src_channel, dst_channel, dst_native_type, value):
 223     '''Generate the expression to clamp the value in the source type to the
 224     destination type range.'''
 225
 226     if src_channel == dst_channel:
 227         return value
 228
 229     src_min = src_channel.min()
 230     src_max = src_channel.max()
 231     dst_min = dst_channel.min()
 232     dst_max = dst_channel.max()
 233
 234     # Translate the destination range to the src native value
 235     dst_min_native = value_to_native(src_channel, dst_min)
 236     dst_max_native = value_to_native(src_channel, dst_max)
 237
 238     if src_min < dst_min and src_max > dst_max:
 239         return 'CLAMP(%s, %s, %s)' % (value, dst_min_native, dst_max_native)
 240
 241     if src_max > dst_max:
 242         return 'MIN2(%s, %s)' % (value, dst_max_native)
 243
 244     if src_min < dst_min:
 245         return 'MAX2(%s, %s)' % (value, dst_min_native)
 246
 247     return value
 248
 249
 250 def conversion_expr(src_channel,
 251                     dst_channel, dst_native_type,
 252                     value,
 253                     clamp=True,
 254                     src_colorspace = 'rgb',
 255                     dst_colorspace = 'rgb'):
 256     '''Generate the expression to convert a value between two types.'''
 257
 258     if src_colorspace != dst_colorspace:
 259         if src_colorspace == 'srgb':
 260             assert src_channel.type == UNSIGNED
 261             assert src_channel.norm
 262             assert src_channel.size == 8
 263             assert dst_colorspace == 'rgb'
 264             if dst_channel.type == FLOAT:
 265                 return 'util_format_srgb_8unorm_to_linear_float(%s)' % value
 266             else:
 267                 assert dst_channel.type == UNSIGNED
 268                 assert dst_channel.norm
 269                 assert dst_channel.size == 8
 270                 return 'util_format_srgb_to_linear_8unorm(%s)' % value
 271         elif dst_colorspace == 'srgb':
 272             assert dst_channel.type == UNSIGNED
 273             assert dst_channel.norm
 274             assert dst_channel.size == 8
 275             assert src_colorspace == 'rgb'
 276             if src_channel.type == FLOAT:
 277                 return 'util_format_linear_float_to_srgb_8unorm(%s)' % value
 278             else:
 279                 assert src_channel.type == UNSIGNED
 280                 assert src_channel.norm
 281                 assert src_channel.size == 8
 282                 return 'util_format_linear_to_srgb_8unorm(%s)' % value
 283         elif src_colorspace == 'zs':
 284             pass
 285         elif dst_colorspace == 'zs':
 286             pass
 287         else:
 288             assert 0
 289
 290     if src_channel == dst_channel:
 291         return value
 292
 293     src_type = src_channel.type
 294     src_size = src_channel.size
 295     src_norm = src_channel.norm
 296
 297     # Promote half to float
 298     if src_type == FLOAT and src_size == 16:
 299         value = 'util_half_to_float(%s)' % value
 300         src_size = 32
 301
 302     if clamp:
 303         if dst_channel.type != FLOAT or src_type != FLOAT:
 304             value = clamp_expr(src_channel, dst_channel, dst_native_type, value)
 305
 306     if src_type in (SIGNED, UNSIGNED) and dst_channel.type in (SIGNED, UNSIGNED):
 307         if not src_norm and not dst_channel.norm:
 308             # neither is normalized -- just cast
 309             return '(%s)%s' % (dst_native_type, value)
 310
 311         src_one = get_one(src_channel)
 312         dst_one = get_one(dst_channel)
 313
 314         if src_one > dst_one and src_norm and dst_channel.norm:
 315             # We can just bitshift
 316             src_shift = get_one_shift(src_channel)
 317             dst_shift = get_one_shift(dst_channel)
 318             value = '(%s >> %s)' % (value, src_shift - dst_shift)
 319         else:
 320             # We need to rescale using an intermediate type big enough to hold the multiplication of both
 321             tmp_native_type = intermediate_native_type(src_size + dst_channel.size, src_channel.sign and dst_channel.sign)
 322             value = '((%s)%s)' % (tmp_native_type, value)
 323             value = '(%s * 0x%x / 0x%x)' % (value, dst_one, src_one)
 324         value = '(%s)%s' % (dst_native_type, value)
 325         return value
 326
 327     # Promote to either float or double
 328     if src_type != FLOAT:
 329         if src_norm or src_type == FIXED:
 330             one = get_one(src_channel)
 331             if src_size <= 23:
 332                 value = '(%s * (1.0f/0x%x))' % (value, one)
 333                 if dst_channel.size <= 32:
 334                     value = '(float)%s' % value
 335                 src_size = 32
 336             else:
 337                 # bigger than single precision mantissa, use double
 338                 value = '(%s * (1.0/0x%x))' % (value, one)
 339                 src_size = 64
 340             src_norm = False
 341         else:
 342             if src_size <= 23 or dst_channel.size <= 32:
 343                 value = '(float)%s' % value
 344                 src_size = 32
 345             else:
 346                 # bigger than single precision mantissa, use double
 347                 value = '(double)%s' % value
 348                 src_size = 64
 349         src_type = FLOAT
 350
 351     # Convert double or float to non-float
 352     if dst_channel.type != FLOAT:
 353         if dst_channel.norm or dst_channel.type == FIXED:
 354             dst_one = get_one(dst_channel)
 355             if dst_channel.size <= 23:
 356                 value = '(%s * 0x%x)' % (value, dst_one)
 357             else:
 358                 # bigger than single precision mantissa, use double
 359                 value = '(%s * (double)0x%x)' % (value, dst_one)
 360         value = '(%s)%s' % (dst_native_type, value)
 361     else:
 362         # Cast double to float when converting to either half or float
 363         if dst_channel.size <= 32 and src_size > 32:
 364             value = '(float)%s' % value
 365             src_size = 32
 366
 367         if dst_channel.size == 16:
 368             value = 'util_float_to_half(%s)' % value
 369         elif dst_channel.size == 64 and src_size < 64:
 370             value = '(double)%s' % value
 371
 372     return value
 373
 374
 375 def generate_unpack_kernel(format, dst_channel, dst_native_type):
 376
 377     if not is_format_supported(format):
 378         return
 379
 380     assert format.layout == PLAIN
 381
 382     src_native_type = native_type(format)
 383
 384     if format.is_bitmask():
 385         depth = format.block_size()
 386         print '         uint%u_t value = *(const uint%u_t *)src;' % (depth, depth)
 387
 388         # Declare the intermediate variables
 389         for i in range(format.nr_channels()):
 390             src_channel = format.channels[i]
 391             if src_channel.type == UNSIGNED:
 392                 print '         uint%u_t %s;' % (depth, src_channel.name)
 393             elif src_channel.type == SIGNED:
 394                 print '         int%u_t %s;' % (depth, src_channel.name)
 395
 396         if depth > 8:
 397             print '#ifdef PIPE_ARCH_BIG_ENDIAN'
 398             print '         value = util_bswap%u(value);' % depth
 399             print '#endif'
 400
 401         # Compute the intermediate unshifted values
 402         shift = 0
 403         for i in range(format.nr_channels()):
 404             src_channel = format.channels[i]
 405             value = 'value'
 406             if src_channel.type == UNSIGNED:
 407                 if shift:
 408                     value = '%s >> %u' % (value, shift)
 409                 if shift + src_channel.size < depth:
 410                     value = '(%s) & 0x%x' % (value, (1 << src_channel.size) - 1)
 411             elif src_channel.type == SIGNED:
 412                 if shift + src_channel.size < depth:
 413                     # Align the sign bit
 414                     lshift = depth - (shift + src_channel.size)
 415                     value = '%s << %u' % (value, lshift)
 416                 # Cast to signed
 417                 value = '(int%u_t)(%s) ' % (depth, value)
 418                 if src_channel.size < depth:
 419                     # Align the LSB bit
 420                     rshift = depth - src_channel.size
 421                     value = '(%s) >> %u' % (value, rshift)
 422             else:
 423                 value = None
 424
 425             if value is not None:
 426                 print '         %s = %s;' % (src_channel.name, value)
 427
 428             shift += src_channel.size
 429
 430         # Convert, swizzle, and store final values
 431         for i in range(4):
 432             swizzle = format.swizzles[i]
 433             if swizzle < 4:
 434                 src_channel = format.channels[swizzle]
 435                 src_colorspace = format.colorspace
 436                 if src_colorspace == 'srgb' and i == 3:
 437                     # Alpha channel is linear
 438                     src_colorspace = 'rgb'
 439                 value = src_channel.name
 440                 value = conversion_expr(src_channel,
 441                                         dst_channel, dst_native_type,
 442                                         value,
 443                                         src_colorspace = src_colorspace)
 444             elif swizzle == SWIZZLE_0:
 445                 value = '0'
 446             elif swizzle == SWIZZLE_1:
 447                 value = get_one(dst_channel)
 448             elif swizzle == SWIZZLE_NONE:
 449                 value = '0'
 450             else:
 451                 assert False
 452             print '         dst[%u] = %s; /* %s */' % (i, value, 'rgba'[i])
 453
 454     else:
 455         print '         union util_format_%s pixel;' % format.short_name()
 456         print '         memcpy(&pixel, src, sizeof pixel);'
 457         bswap_format(format)
 458
 459         for i in range(4):
 460             swizzle = format.swizzles[i]
 461             if swizzle < 4:
 462                 src_channel = format.channels[swizzle]
 463                 src_colorspace = format.colorspace
 464                 if src_colorspace == 'srgb' and i == 3:
 465                     # Alpha channel is linear
 466                     src_colorspace = 'rgb'
 467                 value = 'pixel.chan.%s' % src_channel.name
 468                 value = conversion_expr(src_channel,
 469                                         dst_channel, dst_native_type,
 470                                         value,
 471                                         src_colorspace = src_colorspace)
 472             elif swizzle == SWIZZLE_0:
 473                 value = '0'
 474             elif swizzle == SWIZZLE_1:
 475                 value = get_one(dst_channel)
 476             elif swizzle == SWIZZLE_NONE:
 477                 value = '0'
 478             else:
 479                 assert False
 480             print '         dst[%u] = %s; /* %s */' % (i, value, 'rgba'[i])
 481
 482
 483 def generate_pack_kernel(format, src_channel, src_native_type):
 484
 485     if not is_format_supported(format):
 486         return
 487
 488     dst_native_type = native_type(format)
 489
 490     assert format.layout == PLAIN
 491
 492     inv_swizzle = format.inv_swizzles()
 493
 494     if format.is_bitmask():
 495         depth = format.block_size()
 496         print '         uint%u_t value = 0;' % depth
 497
 498         shift = 0
 499         for i in range(4):
 500             dst_channel = format.channels[i]
 501             if inv_swizzle[i] is not None:
 502                 value ='src[%u]' % inv_swizzle[i]
 503                 dst_colorspace = format.colorspace
 504                 if dst_colorspace == 'srgb' and inv_swizzle[i] == 3:
 505                     # Alpha channel is linear
 506                     dst_colorspace = 'rgb'
 507                 value = conversion_expr(src_channel,
 508                                         dst_channel, dst_native_type,
 509                                         value,
 510                                         dst_colorspace = dst_colorspace)
 511                 if dst_channel.type in (UNSIGNED, SIGNED):
 512                     if shift + dst_channel.size < depth:
 513                         value = '(%s) & 0x%x' % (value, (1 << dst_channel.size) - 1)
 514                     if shift:
 515                         value = '(%s) << %u' % (value, shift)
 516                     if dst_channel.type == SIGNED:
 517                         # Cast to unsigned
 518                         value = '(uint%u_t)(%s) ' % (depth, value)
 519                 else:
 520                     value = None
 521                 if value is not None:
 522                     print '         value |= %s;' % (value)
 523
 524             shift += dst_channel.size
 525
 526         if depth > 8:
 527             print '#ifdef PIPE_ARCH_BIG_ENDIAN'
 528             print '         value = util_bswap%u(value);' % depth
 529             print '#endif'
 530
 531         print '         *(uint%u_t *)dst = value;' % depth
 532
 533     else:
 534         print '         union util_format_%s pixel;' % format.short_name()
 535
 536         for i in range(4):
 537             dst_channel = format.channels[i]
 538             width = dst_channel.size
 539             if inv_swizzle[i] is None:
 540                 continue
 541             dst_colorspace = format.colorspace
 542             if dst_colorspace == 'srgb' and inv_swizzle[i] == 3:
 543                 # Alpha channel is linear
 544                 dst_colorspace = 'rgb'
 545             value ='src[%u]' % inv_swizzle[i]
 546             value = conversion_expr(src_channel,
 547                                     dst_channel, dst_native_type,
 548                                     value,
 549                                     dst_colorspace = dst_colorspace)
 550             print '         pixel.chan.%s = %s;' % (dst_channel.name, value)
 551
 552         bswap_format(format)
 553         print '         memcpy(dst, &pixel, sizeof pixel);'
 554
 555
 556 def generate_format_unpack(format, dst_channel, dst_native_type, dst_suffix):
 557     '''Generate the function to unpack pixels from a particular format'''
 558
 559     name = format.short_name()
 560
 561     print 'static INLINE void'
 562     print 'util_format_%s_unpack_%s(%s *dst_row, unsigned dst_stride, const uint8_t *src_row, unsigned src_stride, unsigned width, unsigned height)' % (name, dst_suffix, dst_native_type)
 563     print '{'
 564
 565     if is_format_supported(format):
 566         print '   unsigned x, y;'
 567         print '   for(y = 0; y < height; y += %u) {' % (format.block_height,)
 568         print '      %s *dst = dst_row;' % (dst_native_type)
 569         print '      const uint8_t *src = src_row;'
 570         print '      for(x = 0; x < width; x += %u) {' % (format.block_width,)
 571
 572         generate_unpack_kernel(format, dst_channel, dst_native_type)
 573
 574         print '         src += %u;' % (format.block_size() / 8,)
 575         print '         dst += 4;'
 576         print '      }'
 577         print '      src_row += src_stride;'
 578         print '      dst_row += dst_stride/sizeof(*dst_row);'
 579         print '   }'
 580
 581     print '}'
 582     print
 583
 584
 585 def generate_format_pack(format, src_channel, src_native_type, src_suffix):
 586     '''Generate the function to pack pixels to a particular format'''
 587
 588     name = format.short_name()
 589
 590     print 'static INLINE void'
 591     print 'util_format_%s_pack_%s(uint8_t *dst_row, unsigned dst_stride, const %s *src_row, unsigned src_stride, unsigned width, unsigned height)' % (name, src_suffix, src_native_type)
 592     print '{'
 593
 594     if is_format_supported(format):
 595         print '   unsigned x, y;'
 596         print '   for(y = 0; y < height; y += %u) {' % (format.block_height,)
 597         print '      const %s *src = src_row;' % (src_native_type)
 598         print '      uint8_t *dst = dst_row;'
 599         print '      for(x = 0; x < width; x += %u) {' % (format.block_width,)
 600
 601         generate_pack_kernel(format, src_channel, src_native_type)
 602
 603         print '         src += 4;'
 604         print '         dst += %u;' % (format.block_size() / 8,)
 605         print '      }'
 606         print '      dst_row += dst_stride;'
 607         print '      src_row += src_stride/sizeof(*src_row);'
 608         print '   }'
 609
 610     print '}'
 611     print
 612
 613
 614 def generate_format_fetch(format, dst_channel, dst_native_type, dst_suffix):
 615     '''Generate the function to unpack pixels from a particular format'''
 616
 617     name = format.short_name()
 618
 619     print 'static INLINE void'
 620     print 'util_format_%s_fetch_%s(%s *dst, const uint8_t *src, unsigned i, unsigned j)' % (name, dst_suffix, dst_native_type)
 621     print '{'
 622
 623     if is_format_supported(format):
 624         generate_unpack_kernel(format, dst_channel, dst_native_type)
 625
 626     print '}'
 627     print
 628
 629
 630 def is_format_hand_written(format):
 631     return format.layout in ('s3tc', 'subsampled', 'other') or format.colorspace == ZS
 632
 633
 634 def generate(formats):
 635     print
 636     print '#include "pipe/p_compiler.h"'
 637     print '#include "u_math.h"'
 638     print '#include "u_half.h"'
 639     print '#include "u_format.h"'
 640     print '#include "u_format_other.h"'
 641     print '#include "u_format_srgb.h"'
 642     print '#include "u_format_yuv.h"'
 643     print '#include "u_format_zs.h"'
 644     print
 645
 646     for format in formats:
 647         if not is_format_hand_written(format):
 648
 649             if is_format_supported(format):
 650                 generate_format_type(format)
 651
 652             channel = Channel(FLOAT, False, 32)
 653             native_type = 'float'
 654             suffix = 'rgba_float'
 655
 656             generate_format_unpack(format, channel, native_type, suffix)
 657             generate_format_pack(format, channel, native_type, suffix)
 658             generate_format_fetch(format, channel, native_type, suffix)
 659
 660             channel = Channel(UNSIGNED, True, 8)
 661             native_type = 'uint8_t'
 662             suffix = 'rgba_8unorm'
 663
 664             generate_format_unpack(format, channel, native_type, suffix)
 665             generate_format_pack(format, channel, native_type, suffix)
 666