diff options
| author | gahaas <ahaas@google.com> | 2016-08-22 23:03:37 -0700 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2016-08-22 23:03:37 -0700 |
| commit | 7ff98ec3cd3e36ded268205ed67fa9ea9c4f8a89 (patch) | |
| tree | c0e54bdf8840a5b38d85013574a89c098e7062b7 /AstSemantics.md | |
| parent | 72c34aac8f358f31398687751f7676ab83f059d1 (diff) | |
| download | nanowasm-design-7ff98ec3cd3e36ded268205ed67fa9ea9c4f8a89.tar.gz | |
Make NaN handling more consistent. (#772)
This PR makes the handling of NaNs in the promotion/demotion of floats more consistent to the handling of NaNs in arithmetic operations. Similar to #716, this PR requires that canonical NaNs have to be preserved by promotion/demotion, whereas the promotion/demotion of non-canonical NaNs can result in an arbitrary quiet NaN.
Diffstat (limited to 'AstSemantics.md')
| -rw-r--r-- | AstSemantics.md | 27 |
1 files changed, 11 insertions, 16 deletions
diff --git a/AstSemantics.md b/AstSemantics.md index c7df3aa..0c303e2 100644 --- a/AstSemantics.md +++ b/AstSemantics.md @@ -618,22 +618,17 @@ Promotion and demotion of floating point values always succeed. Demotion of floating point values uses round-to-nearest ties-to-even rounding, and may overflow to infinity or negative infinity as specified by IEEE 754-2008. -If the operand of promotion is a NaN, the result is nondeterministically chosen -between the following: - - a NaN with a nondeterministic sign bit and a fraction field with 1 in the - most significant bit and 0 in the remaining bits. - - a NaN with the sign bit of the operand and a fraction field consisting of - 1 in the most significant bit, followed by all but the most significant - bit of the fraction field of the operand, followed by all 0s. - -If the operand of demotion is a NaN, the result is nondeterministically chosen -between the following: - - a NaN with a nondeterministic sign bit and a fraction field with 1 in the - most significant bit and 0 in the remaining bits. - - a NaN with the sign bit of the operand and a fraction field consisting of - 1 in the most significant bit, followed by all but the most significant bit - of the fraction field of the operand, discarding the least significant bits - that don't fit. +If the operand of promotion or demotion is a NaN, the result is a NaN with the +following sign bit and fraction field (which does not include the implicit +leading digit of the significand): + +- If the fraction fields of the operand consists of 1 in the most significant bit + and 0 in the remaining bits, the result is a NaN with a nondeterministic sign + bit, 1 in the most significant bit of the fraction field, and all zeros in the + remaining bits of the fraction field. +- Otherwise the result is a NaN with a nondeterministic sign bit, 1 in the most + significant bit of the fraction field, and nondeterminsitic values in the + remaining bits of the fraction field. Reinterpretations always succeed. |