Generalize arm_althp to indicate how exp==max should
be handled for the format. Reorganize canonicalize
and uncanon_normal to use a switch statement, allowing
more cases to be added trivially.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
fpu/softfloat.c | 17 ++++++--
fpu/softfloat-parts.c.inc | 92 ++++++++++++++++++++++++---------------
2 files changed, 69 insertions(+), 40 deletions(-)
diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 8740975348..8d8e576757 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -522,7 +522,16 @@ typedef struct {
#define DECOMPOSED_BINARY_POINT 63
#define DECOMPOSED_IMPLICIT_BIT (1ull << DECOMPOSED_BINARY_POINT)
-/* Structure holding all of the relevant parameters for a format.
+/* Format-specific handling of exp == exp_max */
+typedef enum __attribute__((__packed__)) {
+ /* exp==max, frac==0 ? infinity : nan; this is ieee standard. */
+ float_expmax_ieee,
+ /* exp==max is a normal number; no infinity or nan representation. */
+ float_expmax_normal,
+} FloatFmtExpMaxKind;
+
+/*
+ * Structure holding all of the relevant parameters for a format.
* exp_size: the size of the exponent field
* exp_bias: the offset applied to the exponent field
* exp_max: the maximum normalised exponent
@@ -531,7 +540,7 @@ typedef struct {
* The following are computed based the size of fraction
* round_mask: bits below lsb which must be rounded
* The following optional modifiers are available:
- * arm_althp: handle ARM Alternative Half Precision
+ * exp_max_kind: affects how exp == exp_max is interpreted
* has_explicit_bit: has an explicit integer bit; this affects whether
* the float_status floatx80_behaviour handling applies
*/
@@ -542,7 +551,7 @@ typedef struct {
int exp_max;
int frac_size;
int frac_shift;
- bool arm_althp;
+ FloatFmtExpMaxKind exp_max_kind;
bool has_explicit_bit;
uint64_t round_mask;
} FloatFmt;
@@ -566,7 +575,7 @@ static const FloatFmt float16_params = {
static const FloatFmt float16_params_ahp = {
FLOAT_PARAMS(5, 10),
- .arm_althp = true
+ .exp_max_kind = float_expmax_normal,
};
static const FloatFmt bfloat16_params = {
diff --git a/fpu/softfloat-parts.c.inc b/fpu/softfloat-parts.c.inc
index 79b56014ab..455bbf281e 100644
--- a/fpu/softfloat-parts.c.inc
+++ b/fpu/softfloat-parts.c.inc
@@ -227,18 +227,30 @@ static void partsN(canonicalize)(FloatPartsN *p, float_status *status,
p->exp = fmt->frac_shift - fmt->exp_bias
- shift + !has_pseudo_denormals;
}
- } else if (likely(p->exp < fmt->exp_max) || fmt->arm_althp) {
- p->cls = float_class_normal;
- p->exp -= fmt->exp_bias;
- frac_shl(p, fmt->frac_shift);
- p->frac_hi |= DECOMPOSED_IMPLICIT_BIT;
- } else if (likely(frac_eqz(p))) {
- p->cls = float_class_inf;
- } else {
- frac_shl(p, fmt->frac_shift);
- p->cls = (parts_is_snan_frac(p->frac_hi, status)
- ? float_class_snan : float_class_qnan);
+ return;
}
+ if (unlikely(p->exp == fmt->exp_max)) {
+ switch (fmt->exp_max_kind) {
+ case float_expmax_ieee:
+ if (likely(frac_eqz(p))) {
+ p->cls = float_class_inf;
+ } else {
+ frac_shl(p, fmt->frac_shift);
+ p->cls = (parts_is_snan_frac(p->frac_hi, status)
+ ? float_class_snan : float_class_qnan);
+ }
+ return;
+ case float_expmax_normal:
+ break;
+ default:
+ g_assert_not_reached();
+ }
+ }
+
+ p->cls = float_class_normal;
+ p->exp -= fmt->exp_bias;
+ frac_shl(p, fmt->frac_shift);
+ p->frac_hi |= DECOMPOSED_IMPLICIT_BIT;
}
/*
@@ -314,29 +326,37 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
p->frac_lo &= ~round_mask;
}
- if (fmt->arm_althp) {
- /* ARM Alt HP eschews Inf and NaN for a wider exponent. */
- if (unlikely(exp > exp_max)) {
- /* Overflow. Return the maximum normal. */
- flags = float_flag_invalid;
- exp = exp_max;
- frac_allones(p);
- p->frac_lo &= ~round_mask;
- }
- } else if (unlikely(exp >= exp_max)) {
- flags |= float_flag_overflow;
- if (s->rebias_overflow) {
- exp -= fmt->exp_re_bias;
- } else if (overflow_norm) {
- flags |= float_flag_inexact;
- exp = exp_max - 1;
- frac_allones(p);
- p->frac_lo &= ~round_mask;
- } else {
- flags |= float_flag_inexact;
- p->cls = float_class_inf;
- exp = exp_max;
- frac_clear(p);
+ if (unlikely(exp >= exp_max)) {
+ switch (fmt->exp_max_kind) {
+ case float_expmax_ieee:
+ flags |= float_flag_overflow;
+ if (s->rebias_overflow) {
+ exp -= fmt->exp_re_bias;
+ } else if (overflow_norm) {
+ flags |= float_flag_inexact;
+ exp = exp_max - 1;
+ frac_allones(p);
+ p->frac_lo &= ~round_mask;
+ } else {
+ flags |= float_flag_inexact;
+ p->cls = float_class_inf;
+ exp = exp_max;
+ frac_clear(p);
+ }
+ break;
+
+ case float_expmax_normal:
+ if (unlikely(exp > exp_max)) {
+ /* Overflow. Return the maximum normal. */
+ flags = float_flag_invalid;
+ exp = exp_max;
+ frac_allones(p);
+ p->frac_lo &= ~round_mask;
+ }
+ break;
+
+ default:
+ g_assert_not_reached();
}
}
frac_shr(p, frac_shift);
@@ -434,13 +454,13 @@ static void partsN(uncanon)(FloatPartsN *p, float_status *s,
frac_clear(p);
return;
case float_class_inf:
- g_assert(!fmt->arm_althp);
+ assert(fmt->exp_max_kind == float_expmax_ieee);
p->exp = fmt->exp_max;
frac_clear(p);
return;
case float_class_qnan:
case float_class_snan:
- g_assert(!fmt->arm_althp);
+ assert(fmt->exp_max_kind != float_expmax_normal);
p->exp = fmt->exp_max;
frac_shr(p, fmt->frac_shift);
return;
--
2.43.0On Mon, Feb 23, 2026 at 07:21:49PM +1100, Richard Henderson wrote:
> Generalize arm_althp to indicate how exp==max should
> be handled for the format. Reorganize canonicalize
> and uncanon_normal to use a switch statement, allowing
> more cases to be added trivially.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
> fpu/softfloat.c | 17 ++++++--
> fpu/softfloat-parts.c.inc | 92 ++++++++++++++++++++++++---------------
> 2 files changed, 69 insertions(+), 40 deletions(-)
>
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index 8740975348..8d8e576757 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -522,7 +522,16 @@ typedef struct {
> #define DECOMPOSED_BINARY_POINT 63
> #define DECOMPOSED_IMPLICIT_BIT (1ull << DECOMPOSED_BINARY_POINT)
>
> -/* Structure holding all of the relevant parameters for a format.
> +/* Format-specific handling of exp == exp_max */
> +typedef enum __attribute__((__packed__)) {
> + /* exp==max, frac==0 ? infinity : nan; this is ieee standard. */
> + float_expmax_ieee,
> + /* exp==max is a normal number; no infinity or nan representation. */
> + float_expmax_normal,
> +} FloatFmtExpMaxKind;
> +
> +/*
> + * Structure holding all of the relevant parameters for a format.
> * exp_size: the size of the exponent field
> * exp_bias: the offset applied to the exponent field
> * exp_max: the maximum normalised exponent
> @@ -531,7 +540,7 @@ typedef struct {
> * The following are computed based the size of fraction
> * round_mask: bits below lsb which must be rounded
> * The following optional modifiers are available:
> - * arm_althp: handle ARM Alternative Half Precision
> + * exp_max_kind: affects how exp == exp_max is interpreted
> * has_explicit_bit: has an explicit integer bit; this affects whether
> * the float_status floatx80_behaviour handling applies
> */
> @@ -542,7 +551,7 @@ typedef struct {
> int exp_max;
> int frac_size;
> int frac_shift;
> - bool arm_althp;
> + FloatFmtExpMaxKind exp_max_kind;
> bool has_explicit_bit;
> uint64_t round_mask;
> } FloatFmt;
> @@ -566,7 +575,7 @@ static const FloatFmt float16_params = {
>
> static const FloatFmt float16_params_ahp = {
> FLOAT_PARAMS(5, 10),
> - .arm_althp = true
> + .exp_max_kind = float_expmax_normal,
> };
>
> static const FloatFmt bfloat16_params = {
> diff --git a/fpu/softfloat-parts.c.inc b/fpu/softfloat-parts.c.inc
> index 79b56014ab..455bbf281e 100644
> --- a/fpu/softfloat-parts.c.inc
> +++ b/fpu/softfloat-parts.c.inc
> @@ -227,18 +227,30 @@ static void partsN(canonicalize)(FloatPartsN *p, float_status *status,
> p->exp = fmt->frac_shift - fmt->exp_bias
> - shift + !has_pseudo_denormals;
> }
> - } else if (likely(p->exp < fmt->exp_max) || fmt->arm_althp) {
> - p->cls = float_class_normal;
> - p->exp -= fmt->exp_bias;
> - frac_shl(p, fmt->frac_shift);
> - p->frac_hi |= DECOMPOSED_IMPLICIT_BIT;
> - } else if (likely(frac_eqz(p))) {
> - p->cls = float_class_inf;
> - } else {
> - frac_shl(p, fmt->frac_shift);
> - p->cls = (parts_is_snan_frac(p->frac_hi, status)
> - ? float_class_snan : float_class_qnan);
> + return;
> }
> + if (unlikely(p->exp == fmt->exp_max)) {
> + switch (fmt->exp_max_kind) {
> + case float_expmax_ieee:
> + if (likely(frac_eqz(p))) {
> + p->cls = float_class_inf;
> + } else {
> + frac_shl(p, fmt->frac_shift);
> + p->cls = (parts_is_snan_frac(p->frac_hi, status)
> + ? float_class_snan : float_class_qnan);
> + }
> + return;
> + case float_expmax_normal:
> + break;
> + default:
> + g_assert_not_reached();
> + }
> + }
> +
> + p->cls = float_class_normal;
> + p->exp -= fmt->exp_bias;
> + frac_shl(p, fmt->frac_shift);
> + p->frac_hi |= DECOMPOSED_IMPLICIT_BIT;
> }
>
> /*
> @@ -314,29 +326,37 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
> p->frac_lo &= ~round_mask;
> }
>
> - if (fmt->arm_althp) {
> - /* ARM Alt HP eschews Inf and NaN for a wider exponent. */
> - if (unlikely(exp > exp_max)) {
> - /* Overflow. Return the maximum normal. */
> - flags = float_flag_invalid;
> - exp = exp_max;
> - frac_allones(p);
> - p->frac_lo &= ~round_mask;
> - }
> - } else if (unlikely(exp >= exp_max)) {
> - flags |= float_flag_overflow;
> - if (s->rebias_overflow) {
> - exp -= fmt->exp_re_bias;
> - } else if (overflow_norm) {
> - flags |= float_flag_inexact;
> - exp = exp_max - 1;
> - frac_allones(p);
> - p->frac_lo &= ~round_mask;
> - } else {
> - flags |= float_flag_inexact;
> - p->cls = float_class_inf;
> - exp = exp_max;
> - frac_clear(p);
> + if (unlikely(exp >= exp_max)) {
> + switch (fmt->exp_max_kind) {
> + case float_expmax_ieee:
> + flags |= float_flag_overflow;
> + if (s->rebias_overflow) {
> + exp -= fmt->exp_re_bias;
> + } else if (overflow_norm) {
> + flags |= float_flag_inexact;
> + exp = exp_max - 1;
> + frac_allones(p);
> + p->frac_lo &= ~round_mask;
> + } else {
> + flags |= float_flag_inexact;
> + p->cls = float_class_inf;
> + exp = exp_max;
> + frac_clear(p);
> + }
> + break;
> +
> + case float_expmax_normal:
> + if (unlikely(exp > exp_max)) {
> + /* Overflow. Return the maximum normal. */
> + flags = float_flag_invalid;
> + exp = exp_max;
> + frac_allones(p);
> + p->frac_lo &= ~round_mask;
> + }
> + break;
> +
> + default:
> + g_assert_not_reached();
> }
> }
> frac_shr(p, frac_shift);
> @@ -434,13 +454,13 @@ static void partsN(uncanon)(FloatPartsN *p, float_status *s,
> frac_clear(p);
> return;
> case float_class_inf:
> - g_assert(!fmt->arm_althp);
> + assert(fmt->exp_max_kind == float_expmax_ieee);
> p->exp = fmt->exp_max;
> frac_clear(p);
> return;
> case float_class_qnan:
> case float_class_snan:
> - g_assert(!fmt->arm_althp);
> + assert(fmt->exp_max_kind != float_expmax_normal);
> p->exp = fmt->exp_max;
> frac_shr(p, fmt->frac_shift);
> return;
> --
> 2.43.0
>
Reviewed-by: Chao Liu <chao.liu.zevorn@gmail.com>
Thanks,
Chao
© 2016 - 2026 Red Hat, Inc.