interflop-backend-vprec

Arguments

The VPREC backend simulates any floating-point formats that can fit into the IEEE-754 double precision format with a round to the nearest. The backend allows modifying the bit length of the exponent (range) and the pseudo-mantissa (precision).

Usage: libinterflop_vprec.so [OPTION...]

  -m, --mode=MODE            select VPREC mode among {ieee, full, ib, ob}
      --precision-binary32=PRECISION
                             select precision for binary32 (PRECISION >= 0)
      --precision-binary64=PRECISION
                             select precision for binary64 (PRECISION >= 0)
      --range-binary32=RANGE select range for binary32 (0 < RANGE && RANGE <=
                             8)
      --range-binary64=RANGE select range for binary64 (0 < RANGE && RANGE <=
                             11)
      --error-mode=ERR_MODE  select error mode among (rel, abs, all)
      --max-abs-error-exponent=ERR_EXPONENT
                             select the magnitude of the maximum allowed
                             absolute error (this option is only used when
                             error-mode={abs, all})
  -d, --daz                  denormals-are-zero: sets denormals inputs to zero
  -f, --ftz                  flush-to-zero: sets denormal output to zero
  -?, --help                 Give this help list
      --usage                Give a short usage message

Three options control the behavior of the VPREC backend.

The option --mode=MODE controls the arithmetic error mode. It accepts the following case insensitive values:

• ieee: the program uses standard IEEE arithmetic, no rounding are introduced
• ib: InBound precision only
• ob: OutBound precision only (default mode)
• full: Inbound and outbound mode combined

The option --precision-binary64=PRECISION controls the pseudo-mantissa bit length of the new tested format for floating-point operations in double precision (respectively for single precision with --precision-binary32). It accepts an integer value that represents the precision at which the rounding will be done.

The option --range-binary64=PRECISION controls the exponent bit length of the new tested format for floating-point operations in double precision (respectively for single precision with --range-binary32). It accepts an integer value that represents the magnitude of the numbers.

The option --error-mode=ERR_MODE controls the way in which the error is interpreted. It accepts the following modes:

• rel: (default mode) the error is specified relative to the magnitude of the floating-point number
• abs: the error threshold is specified as an absolute value, independent of the value of the floating-point number, to be interpreted as 2^ERR_EXPONENT
• all: both relative and absolute modes are active simultaneously

The option --max-abs-error-exponent=ERR_EXPONENT is used only when the option --error-mode=ERR_MODE is active and controls the magnitude of the error threshold, when in absolute error mode or all mode. The error thershold is set to 2^ERR_EXPONENT.

A detailed description of the backend is given here.

The following example shows the computation with single precision and the simulation of the bfloat16 format with VPREC:

   $ VFC_BACKENDS="libinterflop_vprec.so --precision-binary32=23 --range-binary32=8" ./a.out
   (2.903225*2.903225)*16384.000000 = 138096.062500
   $ VFC_BACKENDS="libinterflop_vprec.so --precision-binary32=10 --range-binary32=5" ./a.out
   (2.903225*2.903225)*16384.000000 = inf