On Thu, Oct 18, 2012 at 09:53:20AM +0800, Jia Liu wrote: > Hi Aurelien, > > On Wed, Oct 17, 2012 at 11:15 PM, Aurelien Jarno <aurel...@aurel32.net> wrote: > > On Wed, Oct 17, 2012 at 11:39:00AM +0800, Jia Liu wrote: > >> Hi Aurelien, > >> > >> On Wed, Oct 17, 2012 at 7:20 AM, Aurelien Jarno <aurel...@aurel32.net> > >> wrote: > >> > On Tue, Oct 16, 2012 at 12:39:05AM +0800, Jia Liu wrote: > >> >> +/* a[0] is LO, a[1] is HI. */ > >> >> +static inline void mipsdsp_sat64_acc_sub_q63(int64_t *ret, > >> >> + int32_t ac, > >> >> + int64_t *a, > >> >> + CPUMIPSState *env) > >> >> +{ > >> >> + uint32_t temp64, temp63; > >> >> + int64_t temp[2]; > >> >> + int64_t acc[2]; > >> >> + int64_t temp_sum; > >> >> + > >> >> + temp[0] = a[0]; > >> >> + temp[1] = a[1]; > >> >> + > >> >> + acc[0] = env->active_tc.LO[ac]; > >> >> + acc[1] = env->active_tc.HI[ac]; > >> >> + > >> >> + temp_sum = acc[0] - temp[0]; > >> >> + if (MIPSDSP_OVERFLOW(acc[0], -temp[0], temp_sum, > >> >> 0x8000000000000000ull)) { > >> >> + acc[1] -= 1; > >> >> + } > >> >> + acc[0] = temp_sum; > >> >> + > >> >> + temp_sum = acc[1] - temp[1]; > >> >> + acc[1] = temp_sum; > >> >> + > >> >> + temp64 = acc[1] & 0x01; > >> >> + temp63 = (acc[0] >> 63) & 0x01; > >> >> + > >> >> + /* MIPSDSP_OVERFLOW only can check if a 64 bits sub is overflow, > >> >> + * there are two 128 bits value subed then check the 63/64 bits > >> >> are equal > >> >> + * or not.*/ > >> > > >> > If you disagree with what I say, you can send mail, there is no need to > >> > put it as a comment. > >> > > >> > That said MIPSDSP_OVERFLOW doesn't work only on 64-bit values, it can > >> > work other size, as it is done elsewhere in this patch. The only thing > >> > it checked is the highest bit of the two arguments and the result. > >> > Therefore if you pass the highest part of the values, it can work. > >> > > >> > >> I did agree with you, just didn't totally get your point. > >> > >> MIPSDSP_OVERFLOW used to check overflow, but here, 128bit + 128bit, > >> low 64bit overflow need to be checked, so, in fact, I'm not sure what > >> should do. Is this code right? > >> > >> static inline void mipsdsp_sat64_acc_sub_q63(uint64_t *ret, > >> int32_t ac, > >> uint64_t *a, > >> CPUMIPSState *env) > >> { > >> uint32_t temp64; > >> uint64_t temp[2]; > >> uint64_t acc[2]; > >> > >> temp[0] = a[0]; > >> temp[1] = a[1]; > >> > >> acc[0] = env->active_tc.LO[ac]; > >> acc[1] = env->active_tc.HI[ac]; > >> > >> temp[1] = acc[1] - temp[1]; > >> temp[0] = acc[0] - temp[0]; > >> > >> temp64 = temp[1] & 0x01; > >> > >> if (temp64 ^ MIPSDSP_OVERFLOW(acc[0], temp[0], temp[0], (0x01ull << > >> 63))) { > >> if (temp64 == 1) { > >> ret[0] = (0x01ull << 63); > >> ret[1] = ~0ull; > >> } else { > >> ret[0] = (0x01ull << 63) - 1; > >> ret[1] = 0x00; > >> } > >> set_DSPControl_overflow_flag(1, 16 + ac, env); > >> } else { > >> ret[0] = temp[0]; > >> ret[1] = acc[0] > temp[0] ? temp[1] : temp[1] - 1; > >> } > >> } > >> > > > > I don't think xoring temp64 with MIPSDSP_OVERFLOW is correct. What about > > about something like that (untested): > > > > | static inline void mipsdsp_sat64_acc_sub_q63(uint64_t *ret, > > | int32_t ac, > > | uint64_t *a, > > | CPUMIPSState *env) > > | { > > | ret[0] = env->active_tc.LO[ac] - a[0]; > > | ret[1] = env->active_tc.HI[ac] - a[1]; > > | > > In the MIPS-DSP manual, the function is > > function sat64AccumulateSubQ63( acc1..0, a127..0 ) > temp128..0 ← HI[acc]63 || HI[acc]63..0 || LO[acc]63..0 > temp128..0 ← temp - a127..0 if ( temp64 ≠ temp63 ) then > if ( temp64 = 1 ) then > temp127..0 ← 0xFFFFFFFFFFFFFFFF8000000000000000 > else > temp127..0 ← 0x00000000000000007FFFFFFFFFFFFFFF > endif > DSPControlouflag:16+acc ← 1 endif > return temp127..0 > endfunction sat64AccumulateSubQ63 > > > | if (MIPSDSP_OVERFLOW(env->active_tc.LO[ac], -a[0], ret[0], > > 0x8000000000000000ull)) { > > The bit 64 will influence the overflow of bits 0-63. > That is, if bit 64 is 1, and bits 0-63 overflowed, it won't be caught. > So, if we use this code, it won't be handled. >
I think you are correct, we have to take into account the overflow part, but also the original value of the temp64 bit. > > | if ((ret[1] - 1) & 1) { > > | ret[0] = (0x01ull << 63); > > | ret[1] = ~0ull; > > | } else { > > | ret[0] = (0x01ull << 63) - 1; > > | ret[1] = 0x00; > > | } > > | set_DSPControl_overflow_flag(1, 16 + ac, env); > > | } > > | } > > | > > > > The same applies for the add function, but also to some other places in > > the code. > > > > Also note that you might want to have two version of MIPSDSP_OVERFLOW(), > > one for add (like the current one), and one for sub (without the ^ -1), > > so that you don't have to pass the negative value of the second > > argument. > > > > I think it is not necessary to define a new macro very much, what do > you think about this code? Just little changed. > > /* a[0] is LO, a[1] is HI. */ > static inline void mipsdsp_sat64_acc_add_q63(int64_t *ret, > int32_t ac, > int64_t *a, > CPUMIPSState *env) > { > uint32_t temp64; > > ret[0] = env->active_tc.LO[ac] + a[0]; > ret[1] = env->active_tc.HI[ac] + a[1]; > > temp64 = ret[1] & 0x01; > > if (temp64 ^ MIPSDSP_OVERFLOW(env->active_tc.LO[ac], a[0], ret[0], > (0x01ull << 63))) { > if (temp64 == 1) { > ret[0] = (0x01ull << 63); > ret[1] = ~0ull; > } else { > ret[0] = (0x01ull << 63) - 1; > ret[1] = 0x00; > } > set_DSPControl_overflow_flag(1, 16 + ac, env); > } else { > ret[1] = (((uint64_t)env->active_tc.LO[ac] > (uint64_t)ret[0]) && > ((uint64_t)a[0] > (uint64_t)ret[0])) ? ret[1] : ret[1] + 1; > } > } > > static inline void mipsdsp_sat64_acc_sub_q63(int64_t *ret, > int32_t ac, > int64_t *a, > CPUMIPSState *env) > { > uint32_t temp64; > > ret[0] = env->active_tc.LO[ac] - a[0]; > ret[1] = env->active_tc.HI[ac] - a[1]; > > temp64 = ret[1] & 0x01; > > if (temp64 ^ MIPSDSP_OVERFLOW(env->active_tc.LO[ac], -a[0], ret[0], > (0x01ull << 63))) { > if (temp64 == 1) { > ret[0] = (0x01ull << 63); > ret[1] = ~0ull; > } else { > ret[0] = (0x01ull << 63) - 1; > ret[1] = 0x00; > } > set_DSPControl_overflow_flag(1, 16 + ac, env); > } else { > ret[1] = (uint64_t)env->active_tc.LO[ac] > (uint64_t)ret[0] ? > ret[1] : ret[1] - 1; > } > } > That looks fine to me. That said given it mean we have to propagate the carry, you might want to avoid the else case: | static inline void mipsdsp_sat64_acc_sub_q63(int64_t *ret, | int32_t ac, | int64_t *a, | CPUMIPSState *env) | { | bool temp64; | | ret[0] = env->active_tc.LO[ac] - a[0]; | ret[1] = env->active_tc.HI[ac] - a[1]; | | if (MIPSDSP_OVERFLOW(env->active_tc.LO[ac], -a[0], ret[0], | (0x01ull << 63))) { | ret[1] -= 1; | } | temp64 = ret[1] & 1; | if (temp64 != (ret[0] >> 63)) { | if (temp64) { | ret[0] = (0x01ull << 63); | ret[1] = ~0ull; | } else { | ret[0] = (0x01ull << 63) - 1; | ret[1] = 0x00; | } | set_DSPControl_overflow_flag(1, 16 + ac, env); | } | } -- Aurelien Jarno GPG: 1024D/F1BCDB73 aurel...@aurel32.net http://www.aurel32.net