stillwater-sc / universal / 23670073104

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Committed by web-flow

Commit Message

fix(fixpnt): replace double fallback with full-precision division in saturating path (#610)

* fix(fixpnt): replace double fallback with full-precision blockbinary division in saturating path

The saturating fixpnt::operator/= was silently converting both operands
to IEEE-754 double (52-bit mantissa), performing the division in double,
then converting back. This caused catastrophic precision loss for any
fixpnt wider than 53 bits — e.g. fixpnt<64,32,Saturate> lost 12 bits,
fixpnt<128,64,Saturate> lost 76 bits. The commented-out warning meant
users received no indication of the fallback.

Replace with proper blockbinary accumulator division (matching the
Modulo path) plus saturation clamping (matching operator*= Saturate).

* fix(fixpnt): clamp signed quotient in saturating division and add docstring

Reorder saturation logic: apply rounding and restore sign before
clamping, so negative boundary cases (-maxpos/1, maxneg/1) are
handled correctly. Add docstring to operator/= for coverage.

* fix(cfloat): replace double bottleneck in cross-configuration converting constructor

The cfloat-to-cfloat converting constructor unconditionally marshalled
through IEEE-754 double (53-bit mantissa), silently destroying
precision for any cfloat wider than 53 fraction bits.

Replace with a direct blocktriple-based conversion that:
- Creates a blocktriple sized to the TARGET's fraction width
- Pre-aligns source fraction bits with proper guard/round/sticky
  bit collection for round-to-nearest-even
- Handles normal, subnormal, and max-exponent source values
- Uses the existing convert() infrastructure for encoding
- Falls back to double only for cross-block-type conversions
  with srcFbits <= 52 (lossless), with a static_assert for wider

Verified with exhaustive tests across cfloat<8>, <12>, <16>, <32>
configurations including subnormals and saturating modes.

* Revert "fix(cfloat): replace double bottleneck in cross-configuration converting constructor"

This reverts ... (continued)

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