From 5ef396e2ba865f34a4766dbd60c739fb4bcb4fcc Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Mon, 8 Jun 2020 16:58:23 +0000 Subject: target/i386: reimplement fprem, fprem1 using floatx80 operations The x87 fprem and fprem1 emulation is currently based around conversion to double, which is inherently unsuitable for a good emulation of any floatx80 operation. Reimplement using the soft-float floatx80 remainder operations. Signed-off-by: Joseph Myers Reviewed-by: Richard Henderson Message-Id: Signed-off-by: Paolo Bonzini --- target/i386/fpu_helper.c | 156 +++++++++++++++-------------------------------- 1 file changed, 48 insertions(+), 108 deletions(-) diff --git a/target/i386/fpu_helper.c b/target/i386/fpu_helper.c index e32a2aa..8f34ea9 100644 --- a/target/i386/fpu_helper.c +++ b/target/i386/fpu_helper.c @@ -1313,124 +1313,64 @@ void helper_fxtract(CPUX86State *env) merge_exception_flags(env, old_flags); } -void helper_fprem1(CPUX86State *env) +static void helper_fprem_common(CPUX86State *env, bool mod) { - double st0, st1, dblq, fpsrcop, fptemp; - CPU_LDoubleU fpsrcop1, fptemp1; - int expdif; - signed long long int q; - - st0 = floatx80_to_double(env, ST0); - st1 = floatx80_to_double(env, ST1); - - if (isinf(st0) || isnan(st0) || isnan(st1) || (st1 == 0.0)) { - ST0 = double_to_floatx80(env, 0.0 / 0.0); /* NaN */ - env->fpus &= ~0x4700; /* (C3,C2,C1,C0) <-- 0000 */ - return; - } - - fpsrcop = st0; - fptemp = st1; - fpsrcop1.d = ST0; - fptemp1.d = ST1; - expdif = EXPD(fpsrcop1) - EXPD(fptemp1); - - if (expdif < 0) { - /* optimisation? taken from the AMD docs */ - env->fpus &= ~0x4700; /* (C3,C2,C1,C0) <-- 0000 */ - /* ST0 is unchanged */ - return; - } + uint8_t old_flags = save_exception_flags(env); + uint64_t quotient; + CPU_LDoubleU temp0, temp1; + int exp0, exp1, expdiff; - if (expdif < 53) { - dblq = fpsrcop / fptemp; - /* round dblq towards nearest integer */ - dblq = rint(dblq); - st0 = fpsrcop - fptemp * dblq; + temp0.d = ST0; + temp1.d = ST1; + exp0 = EXPD(temp0); + exp1 = EXPD(temp1); - /* convert dblq to q by truncating towards zero */ - if (dblq < 0.0) { - q = (signed long long int)(-dblq); + env->fpus &= ~0x4700; /* (C3,C2,C1,C0) <-- 0000 */ + if (floatx80_is_zero(ST0) || floatx80_is_zero(ST1) || + exp0 == 0x7fff || exp1 == 0x7fff || + floatx80_invalid_encoding(ST0) || floatx80_invalid_encoding(ST1)) { + ST0 = floatx80_modrem(ST0, ST1, mod, "ient, &env->fp_status); + } else { + if (exp0 == 0) { + exp0 = 1 - clz64(temp0.l.lower); + } + if (exp1 == 0) { + exp1 = 1 - clz64(temp1.l.lower); + } + expdiff = exp0 - exp1; + if (expdiff < 64) { + ST0 = floatx80_modrem(ST0, ST1, mod, "ient, &env->fp_status); + env->fpus |= (quotient & 0x4) << (8 - 2); /* (C0) <-- q2 */ + env->fpus |= (quotient & 0x2) << (14 - 1); /* (C3) <-- q1 */ + env->fpus |= (quotient & 0x1) << (9 - 0); /* (C1) <-- q0 */ } else { - q = (signed long long int)dblq; + /* + * Partial remainder. This choice of how many bits to + * process at once is specified in AMD instruction set + * manuals, and empirically is followed by Intel + * processors as well; it ensures that the final remainder + * operation in a loop does produce the correct low three + * bits of the quotient. AMD manuals specify that the + * flags other than C2 are cleared, and empirically Intel + * processors clear them as well. + */ + int n = 32 + (expdiff % 32); + temp1.d = floatx80_scalbn(temp1.d, expdiff - n, &env->fp_status); + ST0 = floatx80_mod(ST0, temp1.d, &env->fp_status); + env->fpus |= 0x400; /* C2 <-- 1 */ } - - env->fpus &= ~0x4700; /* (C3,C2,C1,C0) <-- 0000 */ - /* (C0,C3,C1) <-- (q2,q1,q0) */ - env->fpus |= (q & 0x4) << (8 - 2); /* (C0) <-- q2 */ - env->fpus |= (q & 0x2) << (14 - 1); /* (C3) <-- q1 */ - env->fpus |= (q & 0x1) << (9 - 0); /* (C1) <-- q0 */ - } else { - env->fpus |= 0x400; /* C2 <-- 1 */ - fptemp = pow(2.0, expdif - 50); - fpsrcop = (st0 / st1) / fptemp; - /* fpsrcop = integer obtained by chopping */ - fpsrcop = (fpsrcop < 0.0) ? - -(floor(fabs(fpsrcop))) : floor(fpsrcop); - st0 -= (st1 * fpsrcop * fptemp); } - ST0 = double_to_floatx80(env, st0); + merge_exception_flags(env, old_flags); } -void helper_fprem(CPUX86State *env) +void helper_fprem1(CPUX86State *env) { - double st0, st1, dblq, fpsrcop, fptemp; - CPU_LDoubleU fpsrcop1, fptemp1; - int expdif; - signed long long int q; - - st0 = floatx80_to_double(env, ST0); - st1 = floatx80_to_double(env, ST1); - - if (isinf(st0) || isnan(st0) || isnan(st1) || (st1 == 0.0)) { - ST0 = double_to_floatx80(env, 0.0 / 0.0); /* NaN */ - env->fpus &= ~0x4700; /* (C3,C2,C1,C0) <-- 0000 */ - return; - } - - fpsrcop = st0; - fptemp = st1; - fpsrcop1.d = ST0; - fptemp1.d = ST1; - expdif = EXPD(fpsrcop1) - EXPD(fptemp1); - - if (expdif < 0) { - /* optimisation? taken from the AMD docs */ - env->fpus &= ~0x4700; /* (C3,C2,C1,C0) <-- 0000 */ - /* ST0 is unchanged */ - return; - } - - if (expdif < 53) { - dblq = fpsrcop / fptemp; /* ST0 / ST1 */ - /* round dblq towards zero */ - dblq = (dblq < 0.0) ? ceil(dblq) : floor(dblq); - st0 = fpsrcop - fptemp * dblq; /* fpsrcop is ST0 */ - - /* convert dblq to q by truncating towards zero */ - if (dblq < 0.0) { - q = (signed long long int)(-dblq); - } else { - q = (signed long long int)dblq; - } - - env->fpus &= ~0x4700; /* (C3,C2,C1,C0) <-- 0000 */ - /* (C0,C3,C1) <-- (q2,q1,q0) */ - env->fpus |= (q & 0x4) << (8 - 2); /* (C0) <-- q2 */ - env->fpus |= (q & 0x2) << (14 - 1); /* (C3) <-- q1 */ - env->fpus |= (q & 0x1) << (9 - 0); /* (C1) <-- q0 */ - } else { - int N = 32 + (expdif % 32); /* as per AMD docs */ + helper_fprem_common(env, false); +} - env->fpus |= 0x400; /* C2 <-- 1 */ - fptemp = pow(2.0, (double)(expdif - N)); - fpsrcop = (st0 / st1) / fptemp; - /* fpsrcop = integer obtained by chopping */ - fpsrcop = (fpsrcop < 0.0) ? - -(floor(fabs(fpsrcop))) : floor(fpsrcop); - st0 -= (st1 * fpsrcop * fptemp); - } - ST0 = double_to_floatx80(env, st0); +void helper_fprem(CPUX86State *env) +{ + helper_fprem_common(env, true); } void helper_fyl2xp1(CPUX86State *env) -- cgit v1.1