From 4724bbd28475210d25e0c949a7f424550487b187 Mon Sep 17 00:00:00 2001 From: "Lucas Mateus Castro (alqotel)" Date: Wed, 25 May 2022 10:49:50 -0300 Subject: [PATCH] host-utils: Implemented unsigned 256-by-128 division Based on already existing QEMU implementation, created an unsigned 256 bit by 128 bit division needed to implement the vector divide extended unsigned instruction from PowerISA3.1 Signed-off-by: Lucas Mateus Castro (alqotel) Reviewed-by: Richard Henderson Message-Id: <20220525134954.85056-5-lucas.araujo@eldorado.org.br> Signed-off-by: Daniel Henrique Barboza --- include/qemu/host-utils.h | 2 + include/qemu/int128.h | 38 +++++++++++ util/host-utils.c | 129 ++++++++++++++++++++++++++++++++++++++ 3 files changed, 169 insertions(+) diff --git a/include/qemu/host-utils.h b/include/qemu/host-utils.h index f19bd29105..9767af7573 100644 --- a/include/qemu/host-utils.h +++ b/include/qemu/host-utils.h @@ -32,6 +32,7 @@ #include "qemu/compiler.h" #include "qemu/bswap.h" +#include "qemu/int128.h" #ifdef CONFIG_INT128 static inline void mulu64(uint64_t *plow, uint64_t *phigh, @@ -849,4 +850,5 @@ static inline uint64_t udiv_qrnnd(uint64_t *r, uint64_t n1, #endif } +Int128 divu256(Int128 *plow, Int128 *phigh, Int128 divisor); #endif diff --git a/include/qemu/int128.h b/include/qemu/int128.h index ef71f56e3f..d2b76ca6ac 100644 --- a/include/qemu/int128.h +++ b/include/qemu/int128.h @@ -128,11 +128,21 @@ static inline bool int128_ge(Int128 a, Int128 b) return a >= b; } +static inline bool int128_uge(Int128 a, Int128 b) +{ + return ((__uint128_t)a) >= ((__uint128_t)b); +} + static inline bool int128_lt(Int128 a, Int128 b) { return a < b; } +static inline bool int128_ult(Int128 a, Int128 b) +{ + return (__uint128_t)a < (__uint128_t)b; +} + static inline bool int128_le(Int128 a, Int128 b) { return a <= b; @@ -177,6 +187,15 @@ static inline Int128 bswap128(Int128 a) #endif } +static inline int clz128(Int128 a) +{ + if (a >> 64) { + return __builtin_clzll(a >> 64); + } else { + return (a) ? __builtin_clzll((uint64_t)a) + 64 : 128; + } +} + static inline Int128 int128_divu(Int128 a, Int128 b) { return (__uint128_t)a / (__uint128_t)b; @@ -373,11 +392,21 @@ static inline bool int128_ge(Int128 a, Int128 b) return a.hi > b.hi || (a.hi == b.hi && a.lo >= b.lo); } +static inline bool int128_uge(Int128 a, Int128 b) +{ + return (uint64_t)a.hi > (uint64_t)b.hi || (a.hi == b.hi && a.lo >= b.lo); +} + static inline bool int128_lt(Int128 a, Int128 b) { return !int128_ge(a, b); } +static inline bool int128_ult(Int128 a, Int128 b) +{ + return !int128_uge(a, b); +} + static inline bool int128_le(Int128 a, Int128 b) { return int128_ge(b, a); @@ -418,6 +447,15 @@ static inline Int128 bswap128(Int128 a) return int128_make128(bswap64(a.hi), bswap64(a.lo)); } +static inline int clz128(Int128 a) +{ + if (a.hi) { + return __builtin_clzll(a.hi); + } else { + return (a.lo) ? __builtin_clzll(a.lo) + 64 : 128; + } +} + Int128 int128_divu(Int128, Int128); Int128 int128_remu(Int128, Int128); Int128 int128_divs(Int128, Int128); diff --git a/util/host-utils.c b/util/host-utils.c index 96d5dc0bed..93dfb1b6ab 100644 --- a/util/host-utils.c +++ b/util/host-utils.c @@ -266,3 +266,132 @@ void ulshift(uint64_t *plow, uint64_t *phigh, int32_t shift, bool *overflow) *plow = *plow << shift; } } + +/* + * Unsigned 256-by-128 division. + * Returns the remainder via r. + * Returns lower 128 bit of quotient. + * Needs a normalized divisor (most significant bit set to 1). + * + * Adapted from include/qemu/host-utils.h udiv_qrnnd, + * from the GNU Multi Precision Library - longlong.h __udiv_qrnnd + * (https://gmplib.org/repo/gmp/file/tip/longlong.h) + * + * Licensed under the GPLv2/LGPLv3 + */ +static Int128 udiv256_qrnnd(Int128 *r, Int128 n1, Int128 n0, Int128 d) +{ + Int128 d0, d1, q0, q1, r1, r0, m; + uint64_t mp0, mp1; + + d0 = int128_make64(int128_getlo(d)); + d1 = int128_make64(int128_gethi(d)); + + r1 = int128_remu(n1, d1); + q1 = int128_divu(n1, d1); + mp0 = int128_getlo(q1); + mp1 = int128_gethi(q1); + mulu128(&mp0, &mp1, int128_getlo(d0)); + m = int128_make128(mp0, mp1); + r1 = int128_make128(int128_gethi(n0), int128_getlo(r1)); + if (int128_ult(r1, m)) { + q1 = int128_sub(q1, int128_one()); + r1 = int128_add(r1, d); + if (int128_uge(r1, d)) { + if (int128_ult(r1, m)) { + q1 = int128_sub(q1, int128_one()); + r1 = int128_add(r1, d); + } + } + } + r1 = int128_sub(r1, m); + + r0 = int128_remu(r1, d1); + q0 = int128_divu(r1, d1); + mp0 = int128_getlo(q0); + mp1 = int128_gethi(q0); + mulu128(&mp0, &mp1, int128_getlo(d0)); + m = int128_make128(mp0, mp1); + r0 = int128_make128(int128_getlo(n0), int128_getlo(r0)); + if (int128_ult(r0, m)) { + q0 = int128_sub(q0, int128_one()); + r0 = int128_add(r0, d); + if (int128_uge(r0, d)) { + if (int128_ult(r0, m)) { + q0 = int128_sub(q0, int128_one()); + r0 = int128_add(r0, d); + } + } + } + r0 = int128_sub(r0, m); + + *r = r0; + return int128_or(int128_lshift(q1, 64), q0); +} + +/* + * Unsigned 256-by-128 division. + * Returns the remainder. + * Returns quotient via plow and phigh. + * Also returns the remainder via the function return value. + */ +Int128 divu256(Int128 *plow, Int128 *phigh, Int128 divisor) +{ + Int128 dhi = *phigh; + Int128 dlo = *plow; + Int128 rem, dhighest; + int sh; + + if (!int128_nz(divisor) || !int128_nz(dhi)) { + *plow = int128_divu(dlo, divisor); + *phigh = int128_zero(); + return int128_remu(dlo, divisor); + } else { + sh = clz128(divisor); + + if (int128_ult(dhi, divisor)) { + if (sh != 0) { + /* normalize the divisor, shifting the dividend accordingly */ + divisor = int128_lshift(divisor, sh); + dhi = int128_or(int128_lshift(dhi, sh), + int128_urshift(dlo, (128 - sh))); + dlo = int128_lshift(dlo, sh); + } + + *phigh = int128_zero(); + *plow = udiv256_qrnnd(&rem, dhi, dlo, divisor); + } else { + if (sh != 0) { + /* normalize the divisor, shifting the dividend accordingly */ + divisor = int128_lshift(divisor, sh); + dhighest = int128_rshift(dhi, (128 - sh)); + dhi = int128_or(int128_lshift(dhi, sh), + int128_urshift(dlo, (128 - sh))); + dlo = int128_lshift(dlo, sh); + + *phigh = udiv256_qrnnd(&dhi, dhighest, dhi, divisor); + } else { + /* + * dhi >= divisor + * Since the MSB of divisor is set (sh == 0), + * (dhi - divisor) < divisor + * + * Thus, the high part of the quotient is 1, and we can + * calculate the low part with a single call to udiv_qrnnd + * after subtracting divisor from dhi + */ + dhi = int128_sub(dhi, divisor); + *phigh = int128_one(); + } + + *plow = udiv256_qrnnd(&rem, dhi, dlo, divisor); + } + + /* + * since the dividend/divisor might have been normalized, + * the remainder might also have to be shifted back + */ + rem = int128_urshift(rem, sh); + return rem; + } +}