[Cfp-interest] WG14 IEEE 754-C binding meeting minutes 2018/07/25

[Fred J. Tydeman]

On Wed, 25 Jul 2018 11:24:55 -0500 Rajan Bhakta wrote:
>
>    Fred: Recheck 'Functions and infinity' issues with 754 draft 238. - 
>

IEEE 754 vs 18661 (and C17) for infinity

Possible global issue:  754 uses an unsigned infinity and C uses +/-infinity.
One such example is: remainder(x,inf) vs remainder(x,+/-inf).
But, a counter example is: cosh(+/-inf) is +inf

I am assuming that 754's unsigned infinity is the same as +/-infinity.

roundeven - ok
round - ok
trunc - ok
ceil - ok
floor - ok
rint - ok

nextup - ok
nextdown - ok
remainder - ok
remquo - ok

quantize - ok
quantum - CFP has: If x is NaN, the result is NaN.
          754 has no mention about NaN.

scaleb - ok
logb - ok

fadd - Do we need to add something to Annex F for fadd(+inf,-inf)?
fsub - Do we need to add something to Annex F for fsub(+inf,+inf)?
fmul - Do we need to add something to Annex F for fmul(0,inf)? 
fdiv - Do we need to add something to Annex F for fdiv(inf,inf), fdiv(0,0)?
ffma - Do we need to add something to Annex F for ffma(inf,0,z), ffma(+inf,+y,-inf)?
fsqrt - Do we need to add something to Annex F for fsqrt(-inf)?
convertFromInt - ok

convertToInteger...
 fromfp - ok
 ufromfp - ok
 fromfpx - ok
 ufromfpx - ok
 lround - ok

canonicalize - ok

scanf,... - ok
printf,... - ok

copy - ok
negate - ok
fabs - ok
copysign - ok

encode - ok
decode - ok

compares - ok
iseqsig - ok

is754* - ok

fpclassify - ok
signbit - ok
isnormal - ok
isfinite - ok
iszero - ok
issubnormal - ok
isinf - ok
isnan - ok
issignaling - ok
iscanonical - ok
radix - ok
totalorder - differ for NaN payloads (but not in change to Std C)
totalordermag - differ for NaN payloads (but not in change to Std C)
  Do we need to change the above two to take pointers to floating types,
  so as to not trigger signaling NaNs?

samequantum - ok;  Do we need to worry about signaling NaNs that trigger?

*flags - ok

================

exp - ok
expm1 - ok
exp2 - ok
exp2m1 - ok
exp10 - ok
exp10m1 - ok
log - ok
log2 - ok
log10 - ok
logp1 - ok
log2p1 - ok
log10p1 - ok
hypot - ok
rsqrt - ok
compound - 
 cfp is missing:
   754: compound(+/-0,n) is 1
   754: compound(+inf,n) is +inf for n>0
   754: compound(+inf,n) is +0 for n<0
   754: compound(qNaN,n) is qNaN for n!=0
rootn - 
 replace cfp rootn(+/-inf,n) with
   754: rootn(+inf,n) is +inf for n>0
   754: rootn(+inf,n) is +0 for n<0
   754: rootn(-inf,n) is -inf for odd n>0
   754: rootn(-inf,n) is -0 for odd n<0
   754: rootn(-inf,n) is qNaN and "invalid" for even n>0
   754: rootn(-inf,n) is qNaN and "invalid" for even n<0
pown - 
 replace cfp pown(+/-inf,n) with
   754: pown(+inf,n) is +inf for n>0
   754: pown(+inf,n) is +0 for n<0
   754: pown(-inf,n) is -inf for odd n>0
   754: pown(-inf,n) is +inf for even n>0
   754: pown(-inf,n) is -0 for odd n<0
   754: pown(-inf,n) is +0 for even n<0
pow - 
 754: pow(+/-0,-inf) no exception
 cfp: pow(+/-0,-inf) may raise div-by-zero
powr - 
 cfp is missing:
   powr(x,qNaN) is qNaN for x>=0
   powr(qNaN,y) is qNaN
sin - ok
cos - ok
tan - ok
sinpi - ok
cospi - ok
tanpi - ok
asin - ok
acos - ok
atan - ok
atan2 - ok
asinpi - ok
acospi - ok
atanpi - ok
atan2pi - ok
sinh - ok
cosh - ok
tanh - ok
asinh - ok
acosh - ok
atanh - ok

*rounddir - ok
*modes - ok

For the reduction functions, it appears to me that 754 requires
intermediate computations to not overflow or underflow.  That
contradicts [1] in 7.12.13b; but matches F.10.10b [2].

reducsum - 
 754 has: A sum of infinities of different signs signals the invalid
          operation exception.
 CFP has: returns a NaN and raises the "invalid" floating-point
          exception if any two members of array p are infinities with
          different signs.
 One reading of 754's requirement is the running sum and an array
 element are the two items in question.  So, sum([NaN, +inf, -inf],3)
 when process left to right would NOT raise invalid for 754, but must
 raise invalid for CFP.
reducdot - same problem as reducsum.  Also, once a NaN is found, must
 the remaining vector items be done (which might raise invalid)?
reducsumsq - ok
reducsumabs - ok
scaledprod - same issue as reducsum.
scaledprodsum - same issue as reducsum.
scaledproddiff - same issue as reducsum.

augadd - ok
augsub - ok
augmul - ok

min - ok
max - ok
minNum - ok
maxNum - ok
minMag - ok
maxMag - ok
minMagNum - ok
maxMagNum - ok

payload - ok


---
Fred J. Tydeman        Tydeman Consulting
tydeman at tybor.com      Testing, numerics, programming
+1 (702) 608-6093      Vice-chair of PL22.11 (ANSI "C")
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