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target/m68k: implement fetox

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Using a local m68k floatx80_etox()
[copied from previous:
Written by Andreas Grabher for Previous, NeXT Computer Emulator.]

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20180305203910.10391-7-laurent@vivier.eu>
This commit is contained in:
Laurent Vivier 2018-03-05 21:39:08 +01:00
parent 67b453ed73
commit 40ad087330
6 changed files with 327 additions and 0 deletions
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183
target/m68k/softfloat.c
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@ -782,3 +782,186 @@ floatx80 floatx80_log2(floatx80 a, float_status *status)
return a;
}
/*----------------------------------------------------------------------------
| e to x
*----------------------------------------------------------------------------*/
floatx80 floatx80_etox(floatx80 a, float_status *status)
{
flag aSign;
int32_t aExp;
uint64_t aSig;
int8_t user_rnd_mode, user_rnd_prec;
int32_t compact, n, j, k, m, m1;
floatx80 fp0, fp1, fp2, fp3, l2, scale, adjscale;
flag adjflag;
aSig = extractFloatx80Frac(a);
aExp = extractFloatx80Exp(a);
aSign = extractFloatx80Sign(a);
if (aExp == 0x7FFF) {
if ((uint64_t) (aSig << 1)) {
return propagateFloatx80NaNOneArg(a, status);
}
if (aSign) {
return packFloatx80(0, 0, 0);
}
return packFloatx80(0, floatx80_infinity.high,
floatx80_infinity.low);
}
if (aExp == 0 && aSig == 0) {
return packFloatx80(0, one_exp, one_sig);
}
user_rnd_mode = status->float_rounding_mode;
user_rnd_prec = status->floatx80_rounding_precision;
status->float_rounding_mode = float_round_nearest_even;
status->floatx80_rounding_precision = 80;
adjflag = 0;
if (aExp >= 0x3FBE) { /* |X| >= 2^(-65) */
compact = floatx80_make_compact(aExp, aSig);
if (compact < 0x400CB167) { /* |X| < 16380 log2 */
fp0 = a;
fp1 = a;
fp0 = floatx80_mul(fp0, float32_to_floatx80(
make_float32(0x42B8AA3B), status),
status); /* 64/log2 * X */
adjflag = 0;
n = floatx80_to_int32(fp0, status); /* int(64/log2*X) */
fp0 = int32_to_floatx80(n, status);
j = n & 0x3F; /* J = N mod 64 */
m = n / 64; /* NOTE: this is really arithmetic right shift by 6 */
if (n < 0 && j) {
/* arithmetic right shift is division and
* round towards minus infinity
*/
m--;
}
m += 0x3FFF; /* biased exponent of 2^(M) */
expcont1:
fp2 = fp0; /* N */
fp0 = floatx80_mul(fp0, float32_to_floatx80(
make_float32(0xBC317218), status),
status); /* N * L1, L1 = lead(-log2/64) */
l2 = packFloatx80(0, 0x3FDC, LIT64(0x82E308654361C4C6));
fp2 = floatx80_mul(fp2, l2, status); /* N * L2, L1+L2 = -log2/64 */
fp0 = floatx80_add(fp0, fp1, status); /* X + N*L1 */
fp0 = floatx80_add(fp0, fp2, status); /* R */
fp1 = floatx80_mul(fp0, fp0, status); /* S = R*R */
fp2 = float32_to_floatx80(make_float32(0x3AB60B70),
status); /* A5 */
fp2 = floatx80_mul(fp2, fp1, status); /* fp2 is S*A5 */
fp3 = floatx80_mul(float32_to_floatx80(make_float32(0x3C088895),
status), fp1,
status); /* fp3 is S*A4 */
fp2 = floatx80_add(fp2, float64_to_floatx80(make_float64(
0x3FA5555555554431), status),
status); /* fp2 is A3+S*A5 */
fp3 = floatx80_add(fp3, float64_to_floatx80(make_float64(
0x3FC5555555554018), status),
status); /* fp3 is A2+S*A4 */
fp2 = floatx80_mul(fp2, fp1, status); /* fp2 is S*(A3+S*A5) */
fp3 = floatx80_mul(fp3, fp1, status); /* fp3 is S*(A2+S*A4) */
fp2 = floatx80_add(fp2, float32_to_floatx80(
make_float32(0x3F000000), status),
status); /* fp2 is A1+S*(A3+S*A5) */
fp3 = floatx80_mul(fp3, fp0, status); /* fp3 IS R*S*(A2+S*A4) */
fp2 = floatx80_mul(fp2, fp1,
status); /* fp2 IS S*(A1+S*(A3+S*A5)) */
fp0 = floatx80_add(fp0, fp3, status); /* fp0 IS R+R*S*(A2+S*A4) */
fp0 = floatx80_add(fp0, fp2, status); /* fp0 IS EXP(R) - 1 */
fp1 = exp_tbl[j];
fp0 = floatx80_mul(fp0, fp1, status); /* 2^(J/64)*(Exp(R)-1) */
fp0 = floatx80_add(fp0, float32_to_floatx80(exp_tbl2[j], status),
status); /* accurate 2^(J/64) */
fp0 = floatx80_add(fp0, fp1,
status); /* 2^(J/64) + 2^(J/64)*(Exp(R)-1) */
scale = packFloatx80(0, m, one_sig);
if (adjflag) {
adjscale = packFloatx80(0, m1, one_sig);
fp0 = floatx80_mul(fp0, adjscale, status);
}
status->float_rounding_mode = user_rnd_mode;
status->floatx80_rounding_precision = user_rnd_prec;
a = floatx80_mul(fp0, scale, status);
float_raise(float_flag_inexact, status);
return a;
} else { /* |X| >= 16380 log2 */
if (compact > 0x400CB27C) { /* |X| >= 16480 log2 */
status->float_rounding_mode = user_rnd_mode;
status->floatx80_rounding_precision = user_rnd_prec;
if (aSign) {
a = roundAndPackFloatx80(
status->floatx80_rounding_precision,
0, -0x1000, aSig, 0, status);
} else {
a = roundAndPackFloatx80(
status->floatx80_rounding_precision,
0, 0x8000, aSig, 0, status);
}
float_raise(float_flag_inexact, status);
return a;
} else {
fp0 = a;
fp1 = a;
fp0 = floatx80_mul(fp0, float32_to_floatx80(
make_float32(0x42B8AA3B), status),
status); /* 64/log2 * X */
adjflag = 1;
n = floatx80_to_int32(fp0, status); /* int(64/log2*X) */
fp0 = int32_to_floatx80(n, status);
j = n & 0x3F; /* J = N mod 64 */
/* NOTE: this is really arithmetic right shift by 6 */
k = n / 64;
if (n < 0 && j) {
/* arithmetic right shift is division and
* round towards minus infinity
*/
k--;
}
/* NOTE: this is really arithmetic right shift by 1 */
m1 = k / 2;
if (k < 0 && (k & 1)) {
/* arithmetic right shift is division and
* round towards minus infinity
*/
m1--;
}
m = k - m1;
m1 += 0x3FFF; /* biased exponent of 2^(M1) */
m += 0x3FFF; /* biased exponent of 2^(M) */
goto expcont1;
}
}
} else { /* |X| < 2^(-65) */
status->float_rounding_mode = user_rnd_mode;
status->floatx80_rounding_precision = user_rnd_prec;
a = floatx80_add(a, float32_to_floatx80(make_float32(0x3F800000),
status), status); /* 1 + X */
float_raise(float_flag_inexact, status);
return a;
}
}