interflop-backend-bitmask

Arguments

The Bitmask backend implements a fast first order model of noise. It relies on bitmask operations to achieve low overhead. Unlike MCA backends, the introduced noise is biased, which means that the expected value of the noise is not equal to 0 as explained in Chatelain's thesis, section 2.3.2.

VFC_BACKENDS="libinterflop_bitmask.so --help" ./test
test: verificarlo loaded backend libinterflop_bitmask.so
Usage: libinterflop_bitmask.so [OPTION...]

  -m, --mode=MODE            select BITMASK mode among {ieee, full, ib, ob}
  -o, --operator=OPERATOR    select BITMASK operator among {zero, one, rand}
      --precision-binary32=PRECISION
                             select precision for binary32 (PRECISION > 0)
      --precision-binary64=PRECISION
                             select precision for binary64 (PRECISION > 0)
  -d, --daz                  denormals-are-zero: sets denormals inputs to zero
  -f, --ftz                  flush-to-zero: sets denormal output to zero
  -s, --seed=SEED            fix the random generator seed
  -?, --help                 Give this help list
      --usage                Give a short usage message

Three options control the behavior of the Bitmask backend.

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

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

The option --operator=OPERATOR controls the bitmask operator to apply. It accepts the following case insensitive values:

• zero: sets the last t bits of the mantissa to 0
• one: sets the last t bits of the mantissa to 1
• rand: applies a XOR of random bits to the last t bits of the mantissa (default mode)

Modes zero and one are deterministic and require only one execution. The rand mode is random and must be used like mca backends.

The option --precision-binary64=PRECISION controls the virtual precision used for the floating point operations in double precision (respectively for single precision with --precision-binary32) It accepts an integer value that represents the virtual precision at which MCA operations are performed. Its default value is 53 for binary64 and 24 for binary32. For the Bitmask backend, the virtual precision corresponds to the number of preserved bits in the mantissa.

The option --seed fixes the random generator seed. It should not generally be used except to reproduce a particular Bitmask trace.