From: Jacob Lifshay Date: Thu, 12 Oct 2023 03:29:51 +0000 (-0700) Subject: WIP getting asm version of knuth's algorithm d working X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=9359bf39dfc9a61d5d45415d548f9811a108c28f;p=openpower-isa.git WIP getting asm version of knuth's algorithm d working --- diff --git a/src/openpower/test/bigint/powmod.py b/src/openpower/test/bigint/powmod.py index 6127b604..ea4eb29d 100644 --- a/src/openpower/test/bigint/powmod.py +++ b/src/openpower/test/bigint/powmod.py @@ -294,6 +294,18 @@ def python_divmod_shift_sub_algorithm(n, d, width=256, log_regex=False): return q, r +def divmod2du(RA, RB, RC): + # type: (int, int, int) -> tuple[int, int, bool] + if RC < RB and RB != 0: + RT, RS = divmod(RC << 64 | RA, RB) + overflow = False + else: + overflow = True + RT = (1 << 64) - 1 + RS = 0 + return RT, RS, overflow + + @plain_data() class DivModKnuthAlgorithmD: __slots__ = "num_size", "denom_size", "q_size", "word_size", "regs" @@ -316,7 +328,7 @@ class DivModKnuthAlgorithmD: "n_0": 4, "d_0": 32, "u": 36, - "m": 3, + "m": 9, "v": 32, "n_scalar": 8, "q": 4, @@ -331,8 +343,13 @@ class DivModKnuthAlgorithmD: "t_for_unnorm": 3, "s_for_unnorm": 34, "qhat": 12, - "rhat": 0, - "t_for_prod": 0, + "rhat_lo": 14, + "rhat_hi": 15, + "t_for_prod": 18, + "index": 3, + "j": 11, + "qhat_denom": 18, + "qhat_num_hi": 16, } self.num_size = num_size @@ -411,12 +428,9 @@ class DivModKnuthAlgorithmD: t = u[self.q_size] m = self.q_size do_log(locals(), t="t_single", n=None) + do_log(locals(), m=None) # VL = m, so we don't need it in a GPR for i in reversed(range(m)): - # divmod2du - t <<= self.word_size - t += u[i] - q[i] = t // v[0] - t %= v[0] + q[i], t, _ = divmod2du(u[i], v[0], t) do_log(locals()) r = [0] * self.r_size # remainder r[0] = t @@ -425,7 +439,7 @@ class DivModKnuthAlgorithmD: if m < n: r = [None] * self.r_size # remainder - do_log(locals(), r=("r", self.r_size), n=None) + do_log(locals(), r=("r", self.r_size), m=None, n=None) # dividend < divisor for i in range(self.r_size): r[i] = u[i] @@ -438,10 +452,12 @@ class DivModKnuthAlgorithmD: # calculate amount to shift by -- count leading zeros s = 0 - while (v[n - 1] << s) >> (self.word_size - 1) == 0: + index = n - 1 + do_log(locals(), index="index") + while (v[index] << s) >> (self.word_size - 1) == 0: s += 1 - do_log(locals(), s="s_scalar") + do_log(locals(), s="s_scalar", index=None) if s != 0: on_corner_case("non-zero shift") @@ -467,39 +483,58 @@ class DivModKnuthAlgorithmD: un[i] = t % 2 ** self.word_size t >>= self.word_size do_log(locals()) - un[m] = t + index = m + do_log(locals(), index="index") + un[index] = t - do_log(locals(), u=None, t=None) + do_log(locals(), u=None, t=None, index=None) # Step D2 and Step D7: loop for j in range(min(m - n, self.q_size - 1), -1, -1): + do_log(locals(), j="j") # Step D3: calculate q̂ - t = un[j + n] - t <<= self.word_size - t += un[j + n - 1] - if un[j + n] >= vn[n - 1]: + index = j + n + do_log(locals(), index="index") + qhat_num_hi = un[index] + do_log(locals(), qhat_num_hi="qhat_num_hi") + index = n - 1 + do_log(locals()) + qhat_denom = vn[index] + do_log(locals(), qhat_denom="qhat_denom") + index = j + n - 1 + do_log(locals()) + qhat, rhat_lo, ov = divmod2du(un[index], qhat_denom, qhat_num_hi) + rhat_hi = 0 + do_log(locals(), qhat="qhat", rhat_lo="rhat_lo", rhat_hi="rhat_hi") + if ov: # division overflows word on_corner_case("qhat overflows word") - qhat = 2 ** self.word_size - 1 - rhat = t - qhat * vn[n - 1] - else: - # divmod2du - qhat = t // vn[n - 1] - rhat = t % vn[n - 1] - - do_log(locals(), qhat="qhat", rhat="rhat") + assert qhat_num_hi == qhat_denom + rhat_lo = (qhat * qhat_denom) % 2 ** self.word_size + rhat_hi = (qhat * qhat_denom) >> self.word_size + do_log(locals()) + borrow = un[index] < rhat_lo + rhat_lo = (un[index] - rhat_lo) % 2 ** self.word_size + do_log(locals()) + rhat_hi = qhat_num_hi - rhat_hi - borrow + do_log(locals(), qhat_num_hi=None, qhat_denom=None) - while rhat < 2 ** self.word_size: - if qhat * vn[n - 2] > (rhat << self.word_size) + un[j + n - 2]: + while rhat_hi == 0: + if qhat * vn[n - 2] > (rhat_lo << self.word_size) + un[j + n - 2]: on_corner_case("qhat adjustment") qhat -= 1 - rhat += vn[n - 1] + do_log(locals()) + carry = (rhat_lo + vn[n - 1]) >= 2 ** self.word_size + rhat_lo += vn[n - 1] + rhat_lo %= 2 ** self.word_size + do_log(locals()) + rhat_hi = carry do_log(locals()) else: break - do_log(locals(), rhat=None) + do_log(locals(), rhat_lo=None, rhat_hi=None, index=None) # Step D4: multiply and subtract @@ -549,12 +584,12 @@ class DivModKnuthAlgorithmD: do_log(locals()) # Step D8: un-normalize - do_log(locals(), s="s_for_unnorm", vn=None) + do_log(locals(), s="s_for_unnorm", vn=None, m=None, j=None) r = [0] * self.r_size # remainder do_log(locals(), r=("r", self.r_size), n="n_for_unnorm") # r = un >> s t = 0 - do_log(locals(), t="t_for_unnorm", m=None) + do_log(locals(), t="t_for_unnorm") for i in reversed(range(n)): # dsrd t <<= self.word_size @@ -586,8 +621,13 @@ class DivModKnuthAlgorithmD: t_for_unnorm = self.regs["t_for_unnorm"] s_for_unnorm = self.regs["s_for_unnorm"] qhat = self.regs["qhat"] - rhat = self.regs["rhat"] + rhat_lo = self.regs["rhat_lo"] + rhat_hi = self.regs["rhat_hi"] t_for_prod = self.regs["t_for_prod"] + index = self.regs["index"] + j = self.regs["j"] + qhat_num_hi = self.regs["qhat_num_hi"] + qhat_denom = self.regs["qhat_denom"] num_size = self.num_size denom_size = self.denom_size q_size = self.q_size @@ -600,6 +640,12 @@ class DivModKnuthAlgorithmD: # n in n_0 size num_size # d in d_0 size denom_size + yield "mfspr 0, 8 # mflr 0" + yield "std 0, 16(1)" # save return address + yield "setvl 0, 0, 18, 0, 1, 1" # set VL to 18 + yield "sv.std *14, -144(1)" # save all callee-save registers + yield "stdu 1, -176(1)" # create stack frame as required by ABI + # switch to names used by Knuth's algorithm D yield f"setvl 0, 0, {num_size}, 0, 1, 1" # set VL to num_size yield f"sv.or *{u}, *{n_0}, *{n_0}" # u = n @@ -645,7 +691,7 @@ class DivModKnuthAlgorithmD: # n = denom_size - n yield f"subfic {n_scalar}, {n_scalar}, {denom_size}" - yield f"cmpi 0, 1, {n_scalar}, 1 # cmpi {n_scalar}, 1" + yield f"cmpi 0, 1, {n_scalar}, 1 # cmpdi {n_scalar}, 1" yield "bc 4, 2, divmod_skip_sw_divisor # bne divmod_skip_sw_divisor" # Knuth's algorithm D requires the divisor to have length >= 2 @@ -661,11 +707,68 @@ class DivModKnuthAlgorithmD: yield f"setvl 0, 0, {r_size - 1}, 0, 1, 1" # set VL to r_size - 1 yield f"sv.addi *{r + 1}, 0, 0" # r[1:] = [0] * (r_size - 1) - yield "bclr 20, 0, 0 # blr" + yield "b divmod_return" yield "divmod_skip_sw_divisor:" + yield f"cmp 0, 1, {m}, {n_scalar} # cmpd {m}, {n_scalar}" + yield "bc 4, 0, divmod_skip_copy_r # bge divmod_skip_copy_r" + # if m < n: + + yield f"setvl 0, 0, {r_size}, 0, 1, 1" # set VL to r_size + yield f"sv.or *{r}, *{u}, *{u}" # r[...] = u[...] + yield "b divmod_return" + yield "divmod_skip_copy_r:" + + # Knuth's algorithm D starts here: + + # Step D1: normalize + + # calculate amount to shift by -- count leading zeros + yield f"addi {index}, {n_scalar}, -1" # index = n - 1 + assert index == 3, "index must be r3" + yield f"setvl. 0, 0, {denom_size}, 0, 1, 1" # VL = denom_size + yield f"sv.cntlzd/m=1<= 2 ** 64: - # FIXME: only single-word part of algorithm implemented, - # so we skip the ones that we expect to fail + skip = d >= 2 ** 64 + if n << 64 < n: + skip = False + if skip: + # FIXME: only part of the algorithm is implemented, + # so we skip the cases that we expect to fail continue q, r = divmod(n, d) with self.subTest(n=f"{n:#_x}", d=f"{d:#_x}",