Commit Graph

22 Commits (18911455c6cd7fca3b98af54e95daeeb2f57041d)

Author SHA1 Message Date
Paul Mackerras 7b86bf8863 tests/fpu: Add tests for fdiv and fre with denormalized operands
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
6 months ago
Paul Mackerras 59a7996f1c tests/fpu: Add checks for correct setting of FPRF
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
6 months ago
Paul Mackerras 73cc5167ec Use FPU for division instructions if we have an FPU
- Arrange for XER to be written for OE=1 forms
- Arrange for condition codes to be set for RC=1 forms
  (including correct handling for 32-bit mode)
- Don't instantiate the divider if we have an FPU.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2 years ago
Paul Mackerras f40842d9b2 tests/fpu: Test FPU unavailable interrupt following a load
This adds a load before a floating-point load which should generate a
floating-point unavailable interrupt, to test for the bug where
unavailability interrupts can get dropped while loadstore1 is
executing instructions.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
3 years ago
Paul Mackerras dc1544db69 FPU: Implement floating multiply-add instructions
This implements fmadd, fmsub, fnmadd, fnmsub and their
single-precision counterparts.  The single-precision versions operate
the same as the double-precision versions until the final rounding and
overflow/underflow steps.

This adds an S register to store the low bits of the product.  S
shifts into R on left shifts, and can be negated, but doesn't do any
other arithmetic.

This adds a test for the double-precision versions of these
instructions.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras c350bc1f25 FPU: Implement fsqrt[s] and add a test for fsqrt
This implements the floating square-root calculation using a table
lookup of the inverse square root approximation, followed by three
iterations of Goldschmidt's algorithm, which gives estimates of both
sqrt(FRB) and 1/sqrt(FRB).  Then the residual is calculated as
FRB - R * R and that is multiplied by the 1/sqrt(FRB) estimate to get
an adjustment to R.  The residual and the adjustment can be negative,
and since we have an unsigned multiplier, the upper bits can be wrong.
In practice the adjustment fits into an 8-bit signed value, and the
bottom 8 bits of the adjustment product are correct, so we sign-extend
them, divide by 4 (because R is in 10.54 format) and add them to R.

Finally the residual is calculated again and compared to 2*R+1 to see
if a final increment is needed.  Then the result is rounded and
written back.

This implements fsqrts as fsqrt, but with rounding to single precision
and underflow/overflow calculation using the single-precision exponent
range.  This could be optimized later.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 394f993e75 FPU: Implement frsqrte[s] and a test for frsqrte
This implements frsqrte by table lookup.  We first normalize the input
if necessary and adjust so that the exponent is even, giving us a
mantissa value in the range [1.0, 4.0), which is then used to look up
an entry in a 768-entry table.  The 768 entries are appended to the
table for reciprocal estimates, giving a table of 1024 entries in
total.  frsqrtes is implemented identically to frsqrte.

The estimate supplied is accurate to 1 part in 1024 or better.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras e1bbb786c0 tests/fpu: Add tests for fsel and fcmpu
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 4ad5ab9203 FPU: Implement fre[s]
This just returns the value from the inverse lookup table.  The result
is accurate to better than one part in 512 (the architecture requires
1/256).

This also adds a simple test, which relies on the particular values in
the inverse lookup table, so it is not a general test.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 9cce936251 FPU: Implement fdiv[s]
This implements floating-point division A/B by a process that starts
with normalizing both inputs if necessary.  Then an estimate of 1/B
from a lookup table is refined by 3 Newton-Raphson iterations and then
multiplied by A to get a quotient.  The remainder is calculated as
A - R * B (where R is the result, i.e. the quotient) and the remainder
is compared to 0 and to B to see whether the quotient needs to be
incremented by 1.  The calculations of 1 / B are done with 56 fraction
bits and intermediate results are truncated rather than rounded,
meaning that the final estimate of 1 / B is always correct or a little
bit low, never too high, and thus the calculated quotient is correct
or 1 unit too low.  Doing the estimate of 1 / B with sufficient
precision that the quotient is always correct to the last bit without
needing any adjustment would require many more bits of precision.

This implements fdivs by computing a double-precision quotient and
then rounding it to single precision.  It would be possible to
optimize this by e.g. doing only 2 iterations of Newton-Raphson and
then doing the remainder calculation and adjustment at single
precision rather than double precision.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras e6a5f237bc FPU: Implement fmul[s]
This implements the fmul and fmuls instructions.

For fmul[s] with denormalized operands we normalize the inputs
before doing the multiplication, to eliminate the need for doing
count-leading-zeroes on P.  This adds 3 or 5 cycles to the
execution time when one or both operands are denormalized.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 86b826cd7e FPU: Implement fadd[s] and fsub[s] and add tests for them
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 4807d0bdb6 FPU: Implement fmrgew and fmrgow and add tests for them
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 0ad2aa3014 FPU: Implement floating round-to-integer instructions
This implements frin, friz, frip and frim, and adds tests for them.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 03d1aa968a FPU: Implement floating convert to integer instructions
This implements fctiw, fctiwz, fctiwu, fctiwuz, fctid, fctidz, fctidu
and fctiduz, and adds tests for them.

There are some subtleties around the setting of the inexact (XX) and
invalid conversion (VXCVI) flags in the FPSCR.  If the rounded value
ends up being out of range, we need to set VXCVI and not XX.  For a
conversion to unsigned word or doubleword of a negative value that
rounds to zero, we need to set XX and not VXCVI.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 36130f1db3 tests/fpu: Add tests for frsp
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 9e8fb293ed FPU: Implement floating convert from integer instructions
This implements fcfid, fcfidu, fcfids and fcfidus, which convert
64-bit integer values in an FPR into a floating-point value.
This brings in a lot of the datapath that will be needed in
future, including the shifter, adder, mask generator and
count-leading-zeroes logic, along with the machinery for rounding
to single-precision or double-precision, detecting inexact results,
signalling inexact-result exceptions, and updating result flags
in the FPSCR.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras b628af6176 FPU: Implement fmr and related instructions
This implements fmr, fneg, fabs, fnabs and fcpsgn and adds tests
for them.

This adds logic to unpack and repack floating-point data from the
64-bit packed form (as stored in memory and the register file) into
the unpacked form in the fpr_reg_type record.  This is not strictly
necessary for fmr et al., but will be useful for when we do actual
arithmetic.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras cb27353f37 tests/fpu: Test remaining FPSCR-related instructions
This adds tests for mffsce, mffscrn, mffscrni, mffsl, mcrfs, mtfsfi,
mtfsb0 and mtfsb1.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras bf1d9e9531 tests/fpu: Add tests for basic FPSCR function and interrupt generation
This tests mffs, mtfsf and the generation of floating-point type
program interrupts that occur as a result of mtfsf.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 76ec1a2f0a tests/fpu: Add tests for lfs and stfs instructions
This exercises the single-to-double and double-to-single conversions,
including denormalized cases.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras bcac4b9b2f tests: Add a test for FP loads and stores
This tests that floating-point unavailable exceptions occur as expected
on FP loads and stores, and that the simple FP loads and stores appear
to give reasonable results.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago