9.14 The effects of using flush-to-zero mode in VFP

In flush-to-zero mode, denormalized inputs are treated as zero. Results that are too small to be represented in a normalized number are replaced with zero.

With certain exceptions, flush-to-zero mode has the following effects on floating-point operations:

  • A denormalized number is treated as 0 when used as an input to a floating-point operation. The source register is not altered.
  • If the result of a single-precision floating-point operation, before rounding, is in the range -2-126 to +2-126, it is replaced by 0.
  • If the result of a double-precision floating-point operation, before rounding, is in the range -2-1022 to +2-1022, it is replaced by 0.

In flush-to-zero mode, an Input Denormal exception occurs whenever a denormalized number is used as an operand. An Underflow exception occurs when a result is flushed-to-zero.

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