"Pavan Nikhilesh Bhagavatula" <pbhagavat...@marvell.com> wrote Thursday, March 28, 2019 6:35 AM:
Hi Stefan, Thanks for the heads up, I am planning to use a modified version of https://github.com/hcs0/Hackers-Delight/blob/master/divluh.c.txt for simplicity as we don't require the remainder.
Why don't you refer to the ORIGINAL source <https://www.hackersdelight.org/hdcodetxt/divluh.c.txt> instead? BUT: you also shouldn't use these routines, they too show quite bad implementations of a binary division! As Don Knuth wrote in volume 2 of TAoCP, hardware implementations are most often NOT well-suited for implementation in software. Take a look at the following STRAIGHTFORWARD implementation, both in ANSI C and x86 assembly (for Microsoft's Visual C compiler): unsigned long long divide(unsigned long long dividendlow, unsigned long long dividendhigh, unsigned long long divisor, unsigned long long *remainder) { #ifndef _M_IX86 unsigned int shift = 64; do { if (dividendhigh < divisor) { dividendhigh <<= 1; dividendhigh |= dividendlow >> 63; dividendlow <<= 1; } else { dividendhigh -= divisor; dividendhigh <<= 1; dividendhigh |= dividendlow >> 63; dividendlow <<= 1; dividendlow |= 1; } } while (--shift != 0); if (*remainder != NULL) remainder = dividendhigh; return dividendlow; #else __asm { mov eax, dword ptr dividendlow mov edx, dword ptr dividendlow+4 mov ecx, dword ptr dividendhigh mov ebx, dword ptr dividendhigh+4 mov edi, dword ptr divisor mov esi, dword ptr divisor+4 mov ebp, 64 NEXT: cmp ebx, esi ja SUBTRACT jb SHIFT cmp ecx, edi jb SHIFT SUBTRACT: sub ecx, edi sbb ebx, esi SHIFT: cmc adc eax, eax adc edx, edx adc ecx, ecx adc ebx, ebx dec ebp jnz NEXT or ebp, remainder jz EXIT mov [ebp], ecx mov [ebp+4], ebx EXIT: } #endif }
-----Original Message----- From: dev <dev-boun...@dpdk.org> On Behalf Of Stefan Kanthak Sent: Tuesday, March 26, 2019 6:41 AM To: dev@dpdk.org Cc: han...@stressinduktion.org Subject: [dpdk-dev] [BUG] Maintainer for lib/librte_eal/common/rte_reciprocal.c? Hi @ll, <https://git.dpdk.org/dpdk/plain/MAINTAINERS> does NOT list a maintainer for lib/librte_eal/common/rte_reciprocal.c Whoever it is should take a close look at <https://skanthak.homepage.t- online.de/division.html>, then fix the most obvious bug plus the many deficiencies of divide_128_div_64_to_64(). regards Stefan Kanthak
