[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 1/4] target/arm: Add helpers for FMLAL and FMLSL
From: |
Laurent Desnogues |
Subject: |
Re: [Qemu-devel] [PATCH 1/4] target/arm: Add helpers for FMLAL and FMLSL |
Date: |
Thu, 14 Feb 2019 15:58:10 +0100 |
On Thu, Feb 14, 2019 at 3:56 PM Richard Henderson
<address@hidden> wrote:
>
> On 2/14/19 1:16 AM, Laurent Desnogues wrote:
> > Hello,
> >
> > On Thu, Feb 14, 2019 at 5:00 AM Richard Henderson
> > <address@hidden> wrote:
> >>
> >> Note that float16_to_float32 rightly squashes SNaN to QNaN.
> >> But of course pickNaNMulAdd, for ARM, selects SNaNs first.
> >> So we have to preserve SNaN long enough for the correct NaN
> >> to be selected. Thus float16_to_float32_by_bits.
> >>
> >> Signed-off-by: Richard Henderson <address@hidden>
> >> ---
> >> target/arm/helper.h | 9 +++
> >> target/arm/vec_helper.c | 154 ++++++++++++++++++++++++++++++++++++++++
> >> 2 files changed, 163 insertions(+)
> >>
> >> diff --git a/target/arm/helper.h b/target/arm/helper.h
> >> index 53a38188c6..0302e13604 100644
> >> --- a/target/arm/helper.h
> >> +++ b/target/arm/helper.h
> >> @@ -653,6 +653,15 @@ DEF_HELPER_FLAGS_6(gvec_fmla_idx_s, TCG_CALL_NO_RWG,
> >> DEF_HELPER_FLAGS_6(gvec_fmla_idx_d, TCG_CALL_NO_RWG,
> >> void, ptr, ptr, ptr, ptr, ptr, i32)
> >>
> >> +DEF_HELPER_FLAGS_5(gvec_fmlal_h, TCG_CALL_NO_RWG,
> >> + void, ptr, ptr, ptr, ptr, i32)
> >> +DEF_HELPER_FLAGS_5(gvec_fmlsl_h, TCG_CALL_NO_RWG,
> >> + void, ptr, ptr, ptr, ptr, i32)
> >> +DEF_HELPER_FLAGS_5(gvec_fmlal_idx_h, TCG_CALL_NO_RWG,
> >> + void, ptr, ptr, ptr, ptr, i32)
> >> +DEF_HELPER_FLAGS_5(gvec_fmlsl_idx_h, TCG_CALL_NO_RWG,
> >> + void, ptr, ptr, ptr, ptr, i32)
> >> +
> >> #ifdef TARGET_AARCH64
> >> #include "helper-a64.h"
> >> #include "helper-sve.h"
> >> diff --git a/target/arm/vec_helper.c b/target/arm/vec_helper.c
> >> index 37f338732e..0c3b3de961 100644
> >> --- a/target/arm/vec_helper.c
> >> +++ b/target/arm/vec_helper.c
> >> @@ -766,3 +766,157 @@ DO_FMLA_IDX(gvec_fmla_idx_s, float32, H4)
> >> DO_FMLA_IDX(gvec_fmla_idx_d, float64, )
> >>
> >> #undef DO_FMLA_IDX
> >> +
> >> +/*
> >> + * Convert float16 to float32, raising no exceptions and
> >> + * preserving exceptional values, including SNaN.
> >> + * This is effectively an unpack+repack operation.
> >> + */
> >> +static float32 float16_to_float32_by_bits(uint32_t f16)
> >> +{
> >> + const int f16_bias = 15;
> >> + const int f32_bias = 127;
> >> + uint32_t sign = extract32(f16, 15, 1);
> >> + uint32_t exp = extract32(f16, 10, 5);
> >> + uint32_t frac = extract32(f16, 0, 10);
> >> +
> >> + if (exp == 0x1f) {
> >> + /* Inf or NaN */
> >> + exp = 0xff;
> >> + } else if (exp == 0) {
> >> + /* Zero or denormal. */
> >> + if (frac != 0) {
> >> + /*
> >> + * Denormal; these are all normal float32.
> >> + * Shift the fraction so that the msb is at bit 11,
> >> + * then remove bit 11 as the implicit bit of the
> >> + * normalized float32. Note that we still go through
> >> + * the shift for normal numbers below, to put the
> >> + * float32 fraction at the right place.
> >> + */
> >> + int shift = clz32(frac) - 21;
> >> + frac = (frac << shift) & 0x3ff;
> >> + exp = f32_bias - f16_bias - shift + 1;
> >
> > If FZ16 is set, this should flush to zero.
>
> Ho, hum, yes it should.
>
> > This means you will have to use both fp_status (for the muladd) and
> > fp_status_f16 (for this function) and so you should pass cpu_env to
> > the helpers rather than the fp_status.
>
> It's not quite as simple as that, because aa32 mode would pass
> standard_fp_status. I'll figure something out...
Ha yes, I only looked at AArch64... as usual :-(
Thanks,
Laurent
>
> r~
- [Qemu-devel] [PATCH 0/4] target/arm: Implement ARMv8.2-FHM, Richard Henderson, 2019/02/13
- [Qemu-devel] [PATCH 4/4] target/arm: Enable ARMv8.2-FHM for -cpu max, Richard Henderson, 2019/02/13
- [Qemu-devel] [PATCH 2/4] target/arm: Implement FMLAL and FMLSL for aarch64, Richard Henderson, 2019/02/13
- [Qemu-devel] [PATCH 3/4] target/arm: Implement VFMAL and VFMSL for aarch32, Richard Henderson, 2019/02/13
- Re: [Qemu-devel] [PATCH 0/4] target/arm: Implement ARMv8.2-FHM, no-reply, 2019/02/13
- Re: [Qemu-devel] [PATCH 0/4] target/arm: Implement ARMv8.2-FHM, no-reply, 2019/02/14