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→Floating-Point Behavior: flushing behavior
== Floating-Point Behavior ==
== Floating-Point Behavior ==
The PICA200 is not IEEE-compliant. It has positive and negative infinities and NaN, but does not seem to have negative 0. Several instructions also have behavior that differs from the IEEE functions. Here are the results from some tests done on hardware:
The PICA200 is not IEEE-compliant. It has positive and negative infinities and NaN, but does not seem to have negative 0. Input and output subnormals are flushed to +0. The internal floating point format seems to be the same as used in shader binaries: 1 sign bit, 7 exponent bits, 16 (explicit) mantissa bits. Several instructions also have behavior that differs from the IEEE functions. Here are the results from some tests done on hardware (s = largest subnormal, n = smallest positive normal):
{| class="wikitable" border="1"
{| class="wikitable" border="1"
| min(-inf, +inf)
| min(-inf, +inf)
| -inf
| -inf
|
|
|- style="border-top: double"
| cmp(s, 0)
| false
| cmp does not flush input subnormals
|-
| max(s, 0)
| s
| max does not flush input or output subnormals
|-
| mul(s, 2)
| 0
| input subnormals are flushed in arithmetic instructions
|-
| mul(n, 0.5)
| 0
| output subnormals are flushed in arithmetic instructions
|}
|}
1.0 can be multiplied 63 times by 0.5 until the result compares equal zero. This is consistent with a 7-bit exponent and output subnormal flushing.