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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568b19b32sm4869444f8f.67.2025.06.14.02.54.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 14 Jun 2025 02:54:16 -0700 (PDT) From: David Laight To: Andrew Morton , linux-kernel@vger.kernel.org Cc: David Laight , u.kleine-koenig@baylibre.com, Nicolas Pitre , Oleg Nesterov , Peter Zijlstra , Biju Das Subject: [PATCH v3 next 08/10] lib: mul_u64_u64_div_u64() Separate multiply to a helper for clarity Date: Sat, 14 Jun 2025 10:53:44 +0100 Message-Id: <20250614095346.69130-9-david.laight.linux@gmail.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250614095346.69130-1-david.laight.linux@gmail.com> References: <20250614095346.69130-1-david.laight.linux@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Move the 64x64 => 128 multiply into a static inline helper function for code clarity. No need for the a/b_hi/lo variables, the implicit casts on the function calls do the work for us. Should have minimal effect on the generated code. Signed-off-by: David Laight --- new patch for v3. lib/math/div64.c | 54 +++++++++++++++++++++++++++--------------------- 1 file changed, 30 insertions(+), 24 deletions(-) diff --git a/lib/math/div64.c b/lib/math/div64.c index 2ac7e25039a1..fb77fd9d999d 100644 --- a/lib/math/div64.c +++ b/lib/math/div64.c @@ -193,42 +193,48 @@ static u64 mul_add(u32 a, u32 b, u32 c) return add_u64_u32(mul_u32_u32(a, b), c); } -u64 mul_u64_add_u64_div_u64(u64 a, u64 b, u64 c, u64 d) -{ - if (WARN_ONCE(!d, "%s: division of (%#llx * %#llx + %#llx) by zero, returning 0", - __func__, a, b, c)) { - /* - * Return 0 (rather than ~(u64)0) because it is less likely to - * have unexpected side effects. - */ - return 0; - } - #if defined(__SIZEOF_INT128__) && !defined(test_mul_u64_add_u64_div_u64) - +static inline u64 mul_u64_u64_add_u64(u64 *p_lo, u64 a, u64 b, u64 c) +{ /* native 64x64=128 bits multiplication */ u128 prod = (u128)a * b + c; - u64 n_lo = prod, n_hi = prod >> 64; -#else + *p_lo = prod; + return prod >> 64; +} - /* perform a 64x64=128 bits multiplication manually */ - u32 a_lo = a, a_hi = a >> 32, b_lo = b, b_hi = b >> 32; +#else +static inline u64 mul_u64_u64_add_u64(u64 *p_lo, u64 a, u64 b, u64 c) +{ + /* perform a 64x64=128 bits multiplication in 32bit chunks */ u64 x, y, z; /* Since (x-1)(x-1) + 2(x-1) == x.x - 1 two u32 can be added to a u64 */ - x = mul_add(a_lo, b_lo, c); - y = mul_add(a_lo, b_hi, c >> 32); + x = mul_add(a, b, c); + y = mul_add(a, b >> 32, c >> 32); y = add_u64_u32(y, x >> 32); - z = mul_add(a_hi, b_hi, y >> 32); - y = mul_add(a_hi, b_lo, y); - z = add_u64_u32(z, y >> 32); - x = (y << 32) + (u32)x; - - u64 n_lo = x, n_hi = z; + z = mul_add(a >> 32, b >> 32, y >> 32); + y = mul_add(a >> 32, b, y); + *p_lo = (y << 32) + (u32)x; + return add_u64_u32(z, y >> 32); +} #endif +u64 mul_u64_add_u64_div_u64(u64 a, u64 b, u64 c, u64 d) +{ + u64 n_lo, n_hi; + + if (WARN_ONCE(!d, "%s: division of (%llx * %llx + %llx) by zero, returning 0", + __func__, a, b, c )) { + /* + * Return 0 (rather than ~(u64)0) because it is less likely to + * have unexpected side effects. + */ + return 0; + } + + n_hi = mul_u64_u64_add_u64(&n_lo, a, b, c); if (!n_hi) return div64_u64(n_lo, d); -- 2.39.5