@@ -503,9 +503,8 @@ typedef struct {
bool sign;
} FloatParts;
-#define DECOMPOSED_BINARY_POINT (64 - 2)
+#define DECOMPOSED_BINARY_POINT 63
#define DECOMPOSED_IMPLICIT_BIT (1ull << DECOMPOSED_BINARY_POINT)
-#define DECOMPOSED_OVERFLOW_BIT (DECOMPOSED_IMPLICIT_BIT << 1)
/* Structure holding all of the relevant parameters for a format.
* exp_size: the size of the exponent field
@@ -657,7 +656,7 @@ static FloatParts sf_canonicalize(FloatParts part, const FloatFmt *parm,
part.cls = float_class_zero;
part.frac = 0;
} else {
- int shift = clz64(part.frac) - 1;
+ int shift = clz64(part.frac);
part.cls = float_class_normal;
part.exp = parm->frac_shift - parm->exp_bias - shift + 1;
part.frac <<= shift;
@@ -727,9 +726,8 @@ static FloatParts round_canonical(FloatParts p, float_status *s,
if (likely(exp > 0)) {
if (frac & round_mask) {
flags |= float_flag_inexact;
- frac += inc;
- if (frac & DECOMPOSED_OVERFLOW_BIT) {
- frac >>= 1;
+ if (uadd64_overflow(frac, inc, &frac)) {
+ frac = (frac >> 1) | DECOMPOSED_IMPLICIT_BIT;
exp++;
}
}
@@ -758,9 +756,12 @@ static FloatParts round_canonical(FloatParts p, float_status *s,
p.cls = float_class_zero;
goto do_zero;
} else {
- bool is_tiny = s->tininess_before_rounding
- || (exp < 0)
- || !((frac + inc) & DECOMPOSED_OVERFLOW_BIT);
+ bool is_tiny = s->tininess_before_rounding || (exp < 0);
+
+ if (!is_tiny) {
+ uint64_t discard;
+ is_tiny = !uadd64_overflow(frac, inc, &discard);
+ }
shift64RightJamming(frac, 1 - exp, &frac);
if (frac & round_mask) {
@@ -985,7 +986,7 @@ static FloatParts addsub_floats(FloatParts a, FloatParts b, bool subtract,
a.cls = float_class_zero;
a.sign = s->float_rounding_mode == float_round_down;
} else {
- int shift = clz64(a.frac) - 1;
+ int shift = clz64(a.frac);
a.frac = a.frac << shift;
a.exp = a.exp - shift;
a.sign = a_sign;
@@ -1022,9 +1023,10 @@ static FloatParts addsub_floats(FloatParts a, FloatParts b, bool subtract,
shift64RightJamming(a.frac, b.exp - a.exp, &a.frac);
a.exp = b.exp;
}
- a.frac += b.frac;
- if (a.frac & DECOMPOSED_OVERFLOW_BIT) {
+
+ if (uadd64_overflow(a.frac, b.frac, &a.frac)) {
shift64RightJamming(a.frac, 1, &a.frac);
+ a.frac |= DECOMPOSED_IMPLICIT_BIT;
a.exp += 1;
}
return a;
@@ -1219,16 +1221,17 @@ static FloatParts mul_floats(FloatParts a, FloatParts b, float_status *s)
int exp = a.exp + b.exp;
mul64To128(a.frac, b.frac, &hi, &lo);
- shift128RightJamming(hi, lo, DECOMPOSED_BINARY_POINT, &hi, &lo);
- if (lo & DECOMPOSED_OVERFLOW_BIT) {
- shift64RightJamming(lo, 1, &lo);
+ if (hi & DECOMPOSED_IMPLICIT_BIT) {
exp += 1;
+ } else {
+ hi <<= 1;
}
+ hi |= (lo != 0);
/* Re-use a */
a.exp = exp;
a.sign = sign;
- a.frac = lo;
+ a.frac = hi;
return a;
}
/* handle all the NaN cases */
@@ -1411,56 +1414,41 @@ static FloatParts muladd_floats(FloatParts a, FloatParts b, FloatParts c,
p_exp = a.exp + b.exp;
- /* Multiply of 2 62-bit numbers produces a (2*62) == 124-bit
- * result.
- */
mul64To128(a.frac, b.frac, &hi, &lo);
- /* binary point now at bit 124 */
- /* check for overflow */
- if (hi & (1ULL << (DECOMPOSED_BINARY_POINT * 2 + 1 - 64))) {
- shift128RightJamming(hi, lo, 1, &hi, &lo);
+ /* Renormalize to the msb. */
+ if (hi & DECOMPOSED_IMPLICIT_BIT) {
p_exp += 1;
+ } else {
+ shortShift128Left(hi, lo, 1, &hi, &lo);
}
/* + add/sub */
- if (c.cls == float_class_zero) {
- /* move binary point back to 62 */
- shift128RightJamming(hi, lo, DECOMPOSED_BINARY_POINT, &hi, &lo);
- } else {
+ if (c.cls != float_class_zero) {
int exp_diff = p_exp - c.exp;
if (p_sign == c.sign) {
/* Addition */
if (exp_diff <= 0) {
- shift128RightJamming(hi, lo,
- DECOMPOSED_BINARY_POINT - exp_diff,
- &hi, &lo);
- lo += c.frac;
+ shift64RightJamming(hi, -exp_diff, &hi);
p_exp = c.exp;
+ if (uadd64_overflow(hi, c.frac, &hi)) {
+ shift64RightJamming(hi, 1, &hi);
+ hi |= DECOMPOSED_IMPLICIT_BIT;
+ p_exp += 1;
+ }
} else {
- uint64_t c_hi, c_lo;
- /* shift c to the same binary point as the product (124) */
- c_hi = c.frac >> 2;
- c_lo = 0;
- shift128RightJamming(c_hi, c_lo,
- exp_diff,
- &c_hi, &c_lo);
- add128(hi, lo, c_hi, c_lo, &hi, &lo);
- /* move binary point back to 62 */
- shift128RightJamming(hi, lo, DECOMPOSED_BINARY_POINT, &hi, &lo);
+ uint64_t c_hi, c_lo, over;
+ shift128RightJamming(c.frac, 0, exp_diff, &c_hi, &c_lo);
+ add192(0, hi, lo, 0, c_hi, c_lo, &over, &hi, &lo);
+ if (over) {
+ shift64RightJamming(hi, 1, &hi);
+ hi |= DECOMPOSED_IMPLICIT_BIT;
+ p_exp += 1;
+ }
}
-
- if (lo & DECOMPOSED_OVERFLOW_BIT) {
- shift64RightJamming(lo, 1, &lo);
- p_exp += 1;
- }
-
} else {
/* Subtraction */
- uint64_t c_hi, c_lo;
- /* make C binary point match product at bit 124 */
- c_hi = c.frac >> 2;
- c_lo = 0;
+ uint64_t c_hi = c.frac, c_lo = 0;
if (exp_diff <= 0) {
shift128RightJamming(hi, lo, -exp_diff, &hi, &lo);
@@ -1495,20 +1483,15 @@ static FloatParts muladd_floats(FloatParts a, FloatParts b, FloatParts c,
/* Normalizing to a binary point of 124 is the
correct adjust for the exponent. However since we're
shifting, we might as well put the binary point back
- at 62 where we really want it. Therefore shift as
+ at 63 where we really want it. Therefore shift as
if we're leaving 1 bit at the top of the word, but
adjust the exponent as if we're leaving 3 bits. */
- shift -= 1;
- if (shift >= 64) {
- lo = lo << (shift - 64);
- } else {
- hi = (hi << shift) | (lo >> (64 - shift));
- lo = hi | ((lo << shift) != 0);
- }
- p_exp -= shift - 2;
+ shift128Left(hi, lo, shift, &hi, &lo);
+ p_exp -= shift;
}
}
}
+ hi |= (lo != 0);
if (flags & float_muladd_halve_result) {
p_exp -= 1;
@@ -1518,7 +1501,7 @@ static FloatParts muladd_floats(FloatParts a, FloatParts b, FloatParts c,
a.cls = float_class_normal;
a.sign = p_sign ^ sign_flip;
a.exp = p_exp;
- a.frac = lo;
+ a.frac = hi;
return a;
}
@@ -1742,25 +1725,17 @@ static FloatParts div_floats(FloatParts a, FloatParts b, float_status *s)
* exponent to match.
*
* The udiv_qrnnd algorithm that we're using requires normalization,
- * i.e. the msb of the denominator must be set. Since we know that
- * DECOMPOSED_BINARY_POINT is msb-1, the inputs must be shifted left
- * by one (more), and the remainder must be shifted right by one.
+ * i.e. the msb of the denominator must be set, which is already true.
*/
if (a.frac < b.frac) {
exp -= 1;
- shift128Left(0, a.frac, DECOMPOSED_BINARY_POINT + 2, &n1, &n0);
- } else {
shift128Left(0, a.frac, DECOMPOSED_BINARY_POINT + 1, &n1, &n0);
+ } else {
+ shift128Left(0, a.frac, DECOMPOSED_BINARY_POINT, &n1, &n0);
}
- q = udiv_qrnnd(&r, n1, n0, b.frac << 1);
+ q = udiv_qrnnd(&r, n1, n0, b.frac);
- /*
- * Set lsb if there is a remainder, to set inexact.
- * As mentioned above, to find the actual value of the remainder we
- * would need to shift right, but (1) we are only concerned about
- * non-zero-ness, and (2) the remainder will always be even because
- * both inputs to the division primitive are even.
- */
+ /* Set lsb if there is a remainder, to set inexact. */
a.frac = q | (r != 0);
a.sign = sign;
a.exp = exp;
@@ -2135,12 +2110,12 @@ static FloatParts round_to_int(FloatParts a, FloatRoundMode rmode,
if (a.frac & rnd_mask) {
s->float_exception_flags |= float_flag_inexact;
- a.frac += inc;
- a.frac &= ~rnd_mask;
- if (a.frac & DECOMPOSED_OVERFLOW_BIT) {
+ if (uadd64_overflow(a.frac, inc, &a.frac)) {
a.frac >>= 1;
+ a.frac |= DECOMPOSED_IMPLICIT_BIT;
a.exp++;
}
+ a.frac &= ~rnd_mask;
}
}
break;
@@ -2213,10 +2188,8 @@ static int64_t round_to_int_and_pack(FloatParts in, FloatRoundMode rmode,
case float_class_zero:
return 0;
case float_class_normal:
- if (p.exp < DECOMPOSED_BINARY_POINT) {
+ if (p.exp <= DECOMPOSED_BINARY_POINT) {
r = p.frac >> (DECOMPOSED_BINARY_POINT - p.exp);
- } else if (p.exp - DECOMPOSED_BINARY_POINT < 2) {
- r = p.frac << (p.exp - DECOMPOSED_BINARY_POINT);
} else {
r = UINT64_MAX;
}
@@ -2498,10 +2471,8 @@ static uint64_t round_to_uint_and_pack(FloatParts in, FloatRoundMode rmode,
return 0;
}
- if (p.exp < DECOMPOSED_BINARY_POINT) {
+ if (p.exp <= DECOMPOSED_BINARY_POINT) {
r = p.frac >> (DECOMPOSED_BINARY_POINT - p.exp);
- } else if (p.exp - DECOMPOSED_BINARY_POINT < 2) {
- r = p.frac << (p.exp - DECOMPOSED_BINARY_POINT);
} else {
s->float_exception_flags = orig_flags | float_flag_invalid;
return max;
@@ -2765,11 +2736,11 @@ static FloatParts int_to_float(int64_t a, int scale, float_status *status)
f = -f;
r.sign = true;
}
- shift = clz64(f) - 1;
+ shift = clz64(f);
scale = MIN(MAX(scale, -0x10000), 0x10000);
r.exp = DECOMPOSED_BINARY_POINT - shift + scale;
- r.frac = (shift < 0 ? DECOMPOSED_IMPLICIT_BIT : f << shift);
+ r.frac = f << shift;
}
return r;
@@ -2920,21 +2891,16 @@ bfloat16 int16_to_bfloat16(int16_t a, float_status *status)
static FloatParts uint_to_float(uint64_t a, int scale, float_status *status)
{
FloatParts r = { .sign = false };
+ int shift;
if (a == 0) {
r.cls = float_class_zero;
} else {
scale = MIN(MAX(scale, -0x10000), 0x10000);
+ shift = clz64(a);
r.cls = float_class_normal;
- if ((int64_t)a < 0) {
- r.exp = DECOMPOSED_BINARY_POINT + 1 + scale;
- shift64RightJamming(a, 1, &a);
- r.frac = a;
- } else {
- int shift = clz64(a) - 1;
- r.exp = DECOMPOSED_BINARY_POINT - shift + scale;
- r.frac = a << shift;
- }
+ r.exp = DECOMPOSED_BINARY_POINT - shift + scale;
+ r.frac = a << shift;
}
return r;
@@ -3475,12 +3441,9 @@ static FloatParts sqrt_float(FloatParts a, float_status *s, const FloatFmt *p)
/* We need two overflow bits at the top. Adding room for that is a
* right shift. If the exponent is odd, we can discard the low bit
* by multiplying the fraction by 2; that's a left shift. Combine
- * those and we shift right if the exponent is even.
+ * those and we shift right by 1 if the exponent is odd, otherwise 2.
*/
- a_frac = a.frac;
- if (!(a.exp & 1)) {
- a_frac >>= 1;
- }
+ a_frac = a.frac >> (2 - (a.exp & 1));
a.exp >>= 1;
/* Bit-by-bit computation of sqrt. */
@@ -3488,10 +3451,10 @@ static FloatParts sqrt_float(FloatParts a, float_status *s, const FloatFmt *p)
s_frac = 0;
/* Iterate from implicit bit down to the 3 extra bits to compute a
- * properly rounded result. Remember we've inserted one more bit
- * at the top, so these positions are one less.
+ * properly rounded result. Remember we've inserted two more bits
+ * at the top, so these positions are two less.
*/
- bit = DECOMPOSED_BINARY_POINT - 1;
+ bit = DECOMPOSED_BINARY_POINT - 2;
last_bit = MAX(p->frac_shift - 4, 0);
do {
uint64_t q = 1ULL << bit;
@@ -3507,7 +3470,7 @@ static FloatParts sqrt_float(FloatParts a, float_status *s, const FloatFmt *p)
/* Undo the right shift done above. If there is any remaining
* fraction, the result is inexact. Set the sticky bit.
*/
- a.frac = (r_frac << 1) + (a_frac != 0);
+ a.frac = (r_frac << 2) + (a_frac != 0);
return a;
}
Rather than point the binary point at msb-1, put it at the msb. Use uadd64_overflow to detect when addition overflows instead of DECOMPOSED_OVERFLOW_BIT. This reduces the number of special cases within the code, such as shifting an int64_t either left or right during conversion. Signed-off-by: Richard Henderson <richard.henderson@linaro.org> --- fpu/softfloat.c | 169 +++++++++++++++++++----------------------------- 1 file changed, 66 insertions(+), 103 deletions(-) -- 2.25.1