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target/arm: Fix float16 to/from int16 

The instruction "ucvtf v0.4h, v04h, #2", with input 0x8000u,
overflows the intermediate float16 to infinity before we have a
chance to scale the output.  Use float64 as the intermediate type
so that no input argument (uint32_t in this case) can overflow
or round before scaling.  Given the declared argument, the signed
int32_t function has the same problem.

When converting from float16 to integer, using u/int32_t instead
of u/int16_t means that the bounding is incorrect.

Cc: qemu-stable@nongnu.org
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180502221552.3873-4-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
(cherry picked from commit 88808a022c)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
stable-2.12
Richard Henderson 2018-05-10 18:10:58 +01:00 committed by Michael Roth
parent 0aaf1cca02
commit c708ce7d6e
3 changed files with 55 additions and 6 deletions
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53
target/arm/helper.c
View File

@ -11409,11 +11409,60 @@ VFP_CONV_FIX_A64(sq, s, 32, 64, int64)
VFP_CONV_FIX(uh, s, 32, 32, uint16)
VFP_CONV_FIX(ul, s, 32, 32, uint32)
VFP_CONV_FIX_A64(uq, s, 32, 64, uint64)
VFP_CONV_FIX_A64(sl, h, 16, 32, int32)
VFP_CONV_FIX_A64(ul, h, 16, 32, uint32)
#undef VFP_CONV_FIX
#undef VFP_CONV_FIX_FLOAT
#undef VFP_CONV_FLOAT_FIX_ROUND
#undef VFP_CONV_FIX_A64
/* Conversion to/from f16 can overflow to infinity before/after scaling.
* Therefore we convert to f64 (which does not round), scale,
* and then convert f64 to f16 (which may round).
*/
static float16 do_postscale_fp16(float64 f, int shift, float_status *fpst)
{
return float64_to_float16(float64_scalbn(f, -shift, fpst), true, fpst);
}
float16 HELPER(vfp_sltoh)(uint32_t x, uint32_t shift, void *fpst)
{
return do_postscale_fp16(int32_to_float64(x, fpst), shift, fpst);
}
float16 HELPER(vfp_ultoh)(uint32_t x, uint32_t shift, void *fpst)
{
return do_postscale_fp16(uint32_to_float64(x, fpst), shift, fpst);
}
static float64 do_prescale_fp16(float16 f, int shift, float_status *fpst)
{
if (unlikely(float16_is_any_nan(f))) {
float_raise(float_flag_invalid, fpst);
return 0;
} else {
int old_exc_flags = get_float_exception_flags(fpst);
float64 ret;
ret = float16_to_float64(f, true, fpst);
ret = float64_scalbn(ret, shift, fpst);
old_exc_flags |= get_float_exception_flags(fpst)
& float_flag_input_denormal;
set_float_exception_flags(old_exc_flags, fpst);
return ret;
}
}
uint32_t HELPER(vfp_toshh)(float16 x, uint32_t shift, void *fpst)
{
return float64_to_int16(do_prescale_fp16(x, shift, fpst), fpst);
}
uint32_t HELPER(vfp_touhh)(float16 x, uint32_t shift, void *fpst)
{
return float64_to_uint16(do_prescale_fp16(x, shift, fpst), fpst);
}
/* Set the current fp rounding mode and return the old one.
* The argument is a softfloat float_round_ value.

4
target/arm/helper.h
View File

@ -149,8 +149,8 @@ DEF_HELPER_3(vfp_toshd_round_to_zero, i64, f64, i32, ptr)
DEF_HELPER_3(vfp_tosld_round_to_zero, i64, f64, i32, ptr)
DEF_HELPER_3(vfp_touhd_round_to_zero, i64, f64, i32, ptr)
DEF_HELPER_3(vfp_tould_round_to_zero, i64, f64, i32, ptr)
DEF_HELPER_3(vfp_toulh, i32, f16, i32, ptr)
DEF_HELPER_3(vfp_toslh, i32, f16, i32, ptr)
DEF_HELPER_3(vfp_touhh, i32, f16, i32, ptr)
DEF_HELPER_3(vfp_toshh, i32, f16, i32, ptr)
DEF_HELPER_3(vfp_toshs, i32, f32, i32, ptr)
DEF_HELPER_3(vfp_tosls, i32, f32, i32, ptr)
DEF_HELPER_3(vfp_tosqs, i64, f32, i32, ptr)

4
target/arm/translate-a64.c
View File

@ -7263,9 +7263,9 @@ static void handle_simd_shift_fpint_conv(DisasContext *s, bool is_scalar,
switch (size) {
case MO_16:
if (is_u) {
fn = gen_helper_vfp_toulh;
fn = gen_helper_vfp_touhh;
} else {
fn = gen_helper_vfp_toslh;
fn = gen_helper_vfp_toshh;
}
break;
case MO_32: