From f5ad9c2e0ea60dc5426def7a54f04347a33a952e Mon Sep 17 00:00:00 2001 From: Craig Topper Date: Thu, 10 Sep 2020 06:55:00 -0700 Subject: [PATCH] [builtins] Write __divmoddi4/__divmodsi4 in terms __udivmod instead of __div and multiply. Previously we calculating the remainder by multiplying the quotient and divisor and subtracting from the dividend. __udivmod can calculate the remainder while calculating the quotient. We just need to correct the sign afterward. Reviewed By: MaskRay Differential Revision: https://reviews.llvm.org/D87433 --- compiler-rt/lib/builtins/divmoddi4.c | 13 ++++++++++--- compiler-rt/lib/builtins/divmodsi4.c | 13 ++++++++++--- 2 files changed, 20 insertions(+), 6 deletions(-) diff --git a/compiler-rt/lib/builtins/divmoddi4.c b/compiler-rt/lib/builtins/divmoddi4.c index 7f33351..e7cbbb1 100644 --- a/compiler-rt/lib/builtins/divmoddi4.c +++ b/compiler-rt/lib/builtins/divmoddi4.c @@ -15,7 +15,14 @@ // Returns: a / b, *rem = a % b COMPILER_RT_ABI di_int __divmoddi4(di_int a, di_int b, di_int *rem) { - di_int d = __divdi3(a, b); - *rem = a - (d * b); - return d; + const int bits_in_dword_m1 = (int)(sizeof(di_int) * CHAR_BIT) - 1; + di_int s_a = a >> bits_in_dword_m1; // s_a = a < 0 ? -1 : 0 + di_int s_b = b >> bits_in_dword_m1; // s_b = b < 0 ? -1 : 0 + a = (a ^ s_a) - s_a; // negate if s_a == -1 + b = (b ^ s_b) - s_b; // negate if s_b == -1 + s_b ^= s_a; // sign of quotient + du_int r; + di_int q = (__udivmoddi4(a, b, &r) ^ s_b) - s_b; // negate if s_b == -1 + *rem = (r ^ s_a) - s_a; // negate if s_a == -1 + return q; } diff --git a/compiler-rt/lib/builtins/divmodsi4.c b/compiler-rt/lib/builtins/divmodsi4.c index 402eed2..a85e299 100644 --- a/compiler-rt/lib/builtins/divmodsi4.c +++ b/compiler-rt/lib/builtins/divmodsi4.c @@ -16,7 +16,14 @@ // Returns: a / b, *rem = a % b COMPILER_RT_ABI si_int __divmodsi4(si_int a, si_int b, si_int *rem) { - si_int d = __divsi3(a, b); - *rem = a - (d * b); - return d; + const int bits_in_word_m1 = (int)(sizeof(si_int) * CHAR_BIT) - 1; + si_int s_a = a >> bits_in_word_m1; // s_a = a < 0 ? -1 : 0 + si_int s_b = b >> bits_in_word_m1; // s_b = b < 0 ? -1 : 0 + a = (a ^ s_a) - s_a; // negate if s_a == -1 + b = (b ^ s_b) - s_b; // negate if s_b == -1 + s_b ^= s_a; // sign of quotient + su_int r; + si_int q = (__udivmodsi4(a, b, &r) ^ s_b) - s_b; // negate if s_b == -1 + *rem = (r ^ s_a) - s_a; // negate if s_a == -1 + return q; } -- 2.7.4