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From: "kirdyankinsp at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libgcc/113155] New: large overhead for cast float to uint64_t.
 Arm cortex-m4 (ARMv7E-M, fpv4-sp-d16, ieee 754). Compiler: arm-none-eabi-gcc
Date: Wed, 27 Dec 2023 07:03:02 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113155

            Bug ID: 113155
           Summary: large overhead for cast float to uint64_t. Arm
                    cortex-m4 (ARMv7E-M, fpv4-sp-d16, ieee 754). Compiler:
                    arm-none-eabi-gcc
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgcc
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kirdyankinsp at gmail dot com
  Target Milestone: ---

To cast float to uint64 the initial value first converted to double. Cortex=
-M4
does not have hardware support for "double". Therefore, such an implementat=
ion
adds several kilobytes of code, which is unacceptable for embeded systems w=
ith
limited resources. In addition, increasing the code size is, of course, low
performance.
I think it is necessary to separate the softfloat functions for platforms t=
hat
have hardware "float" support and do not have a hardware "double". The curr=
ent
version cannot be used for embedded systems. Additional functions need to be
written.
Below is the __aeabi_f2ulz code for fpv4-sp-d16 (ieee 754):

uint64_t __aeabi_f2ulz(float f)
{
  uint32_t result =3D *((uint32_t*) &f);
  uint32_t exp;
  result &=3D (~0x80000000);
  exp =3D result >> 23;
  result &=3D 0x7FFFFF;
  result |=3D 0x800000;
#if CHECK_UB
  if (exp =3D=3D 0xFF) // if NaN or inf
  {
    return 0x8000000000000000; // ????????
  }
  if(exp > (0x96 + 40)) // if the variable value is too large
  {
    return 0x8000000000000000; // ????????
  }
#endif
  if (exp < 0x7F)
  {
    return 0;
  }
  if (exp <=3D 0x96U)
  {
    exp =3D 0x96 - exp;
    result >>=3D exp;
    return (uint64_t) result;
  }
  exp -=3D 0x96U;
  return (uint64_t) result << exp;
}=