ARM application development SDK for MNT ZZ9000 graphics and coprocessor card for classic Amiga computers.
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uread4.S 1.3KB

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  1. /* Runtime ABI for the ARM Cortex-M0
  2. * uread4.S: unaligned memory read
  3. *
  4. * Copyright (c) 2017 Jörg Mische <bobbl@gmx.de>
  5. *
  6. * Permission to use, copy, modify, and/or distribute this software for any
  7. * purpose with or without fee is hereby granted, provided that the above
  8. * copyright notice and this permission notice appear in all copies.
  9. *
  10. * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  11. * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  12. * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  13. * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  14. * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  15. * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
  16. * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  17. */
  18. .syntax unified
  19. .text
  20. .thumb
  21. .cpu cortex-m0
  22. @ int __aeabi_uread4(void *r0)
  23. @
  24. @ Read 4 little endian bytes from unaligned memory address
  25. @
  26. .thumb_func
  27. .global __aeabi_uread4
  28. __aeabi_uread4:
  29. lsls r1, r0, #30
  30. lsrs r1, r1, #27 @ r1 = bit offset relative to aligned address
  31. lsrs r0, r0, #2
  32. lsls r0, r0, #2 @ r0 = round down address
  33. ldm r0, {r0,r2} @ r2:r0 = 8 bytes including the unaligned word
  34. lsrs r0, r1
  35. subs r1, #32
  36. negs r1, r1
  37. lsls r2, r1
  38. orrs r0, r2 @ r0 = (r0>>r1) | (r2<<(32-r1))
  39. bx lr