diff options
| -rw-r--r-- | fpu/softfloat-parts.c.inc | 27 | ||||
| -rw-r--r-- | fpu/softfloat.c | 9 | ||||
| -rw-r--r-- | include/fpu/softfloat-types.h | 19 | ||||
| -rw-r--r-- | target/m68k/cpu.c | 3 |
4 files changed, 49 insertions, 9 deletions
diff --git a/fpu/softfloat-parts.c.inc b/fpu/softfloat-parts.c.inc index 1d09f066c5..171bfd06e3 100644 --- a/fpu/softfloat-parts.c.inc +++ b/fpu/softfloat-parts.c.inc @@ -195,6 +195,25 @@ static FloatPartsN *partsN(pick_nan_muladd)(FloatPartsN *a, FloatPartsN *b, static void partsN(canonicalize)(FloatPartsN *p, float_status *status, const FloatFmt *fmt) { + /* + * It's target-dependent how to handle the case of exponent 0 + * and Integer bit set. Intel calls these "pseudodenormals", + * and treats them as if the integer bit was 0, and never + * produces them on output. This is the default behaviour for QEMU. + * For m68k, the integer bit is considered validly part of the + * input value when the exponent is 0, and may be 0 or 1, + * giving extra range. They may also be generated as outputs. + * (The m68k manual actually calls these values part of the + * normalized number range, not the denormalized number range, + * but that distinction is not important for us, because + * m68k doesn't care about the input_denormal_used status flag.) + * floatx80_pseudo_denormal_valid selects the m68k behaviour, + * which changes both how we canonicalize such a value and + * how we uncanonicalize results. + */ + bool has_pseudo_denormals = fmt->has_explicit_bit && + (status->floatx80_behaviour & floatx80_pseudo_denormal_valid); + if (unlikely(p->exp == 0)) { if (likely(frac_eqz(p))) { p->cls = float_class_zero; @@ -206,7 +225,7 @@ static void partsN(canonicalize)(FloatPartsN *p, float_status *status, int shift = frac_normalize(p); p->cls = float_class_denormal; p->exp = fmt->frac_shift - fmt->exp_bias - - shift + !fmt->m68k_denormal; + - shift + !has_pseudo_denormals; } } else if (likely(p->exp < fmt->exp_max) || fmt->arm_althp) { p->cls = float_class_normal; @@ -342,13 +361,15 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s, frac_clear(p); } else { bool is_tiny = s->tininess_before_rounding || exp < 0; + bool has_pseudo_denormals = fmt->has_explicit_bit && + (s->floatx80_behaviour & floatx80_pseudo_denormal_valid); if (!is_tiny) { FloatPartsN discard; is_tiny = !frac_addi(&discard, p, inc); } - frac_shrjam(p, !fmt->m68k_denormal - exp); + frac_shrjam(p, !has_pseudo_denormals - exp); if (p->frac_lo & round_mask) { /* Need to recompute round-to-even/round-to-odd. */ @@ -379,7 +400,7 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s, p->frac_lo &= ~round_mask; } - exp = (p->frac_hi & DECOMPOSED_IMPLICIT_BIT) && !fmt->m68k_denormal; + exp = (p->frac_hi & DECOMPOSED_IMPLICIT_BIT) && !has_pseudo_denormals; frac_shr(p, frac_shift); if (is_tiny) { diff --git a/fpu/softfloat.c b/fpu/softfloat.c index 2a20ae871e..b299cfaf86 100644 --- a/fpu/softfloat.c +++ b/fpu/softfloat.c @@ -537,7 +537,8 @@ typedef struct { * round_mask: bits below lsb which must be rounded * The following optional modifiers are available: * arm_althp: handle ARM Alternative Half Precision - * m68k_denormal: explicit integer bit for extended precision may be 1 + * has_explicit_bit: has an explicit integer bit; this affects whether + * the float_status floatx80_behaviour handling applies */ typedef struct { int exp_size; @@ -547,7 +548,7 @@ typedef struct { int frac_size; int frac_shift; bool arm_althp; - bool m68k_denormal; + bool has_explicit_bit; uint64_t round_mask; } FloatFmt; @@ -600,9 +601,7 @@ static const FloatFmt floatx80_params[3] = { [floatx80_precision_d] = { FLOATX80_PARAMS(52) }, [floatx80_precision_x] = { FLOATX80_PARAMS(64), -#ifdef TARGET_M68K - .m68k_denormal = true, -#endif + .has_explicit_bit = true, }, }; diff --git a/include/fpu/softfloat-types.h b/include/fpu/softfloat-types.h index b1941384ae..1af2a0cb14 100644 --- a/include/fpu/softfloat-types.h +++ b/include/fpu/softfloat-types.h @@ -349,6 +349,25 @@ typedef enum __attribute__((__packed__)) { * and using them as inputs to a float op will raise Invalid. */ floatx80_unnormal_valid = 8, + + /* + * If the exponent is 0 and the Integer bit is set, Intel call + * this a "pseudo-denormal"; x86 supports that only on input + * (treating them as denormals by ignoring the Integer bit). + * For m68k, the integer bit is considered validly part of the + * input value when the exponent is 0, and may be 0 or 1, + * giving extra range. They may also be generated as outputs. + * (The m68k manual actually calls these values part of the + * normalized number range, not the denormalized number range.) + * + * By default you get the Intel behaviour where the Integer + * bit is ignored; if this is set then the Integer bit value + * is honoured, m68k-style. + * + * Either way, floatx80_invalid_encoding() will always accept + * pseudo-denormals. + */ + floatx80_pseudo_denormal_valid = 16, } FloatX80Behaviour; /* diff --git a/target/m68k/cpu.c b/target/m68k/cpu.c index 505fa97a53..2617d8f6ed 100644 --- a/target/m68k/cpu.c +++ b/target/m68k/cpu.c @@ -139,7 +139,8 @@ static void m68k_cpu_reset_hold(Object *obj, ResetType type) set_floatx80_behaviour(floatx80_default_inf_int_bit_is_zero | floatx80_pseudo_inf_valid | floatx80_pseudo_nan_valid | - floatx80_unnormal_valid, + floatx80_unnormal_valid | + floatx80_pseudo_denormal_valid, &env->fp_status); nan = floatx80_default_nan(&env->fp_status); |