/* * arch/s390/lib/div64.c * * __div64_32 implementation for 31 bit. * * Copyright (C) IBM Corp. 2006 * Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com), */ #include <linux/types.h> #include <linux/module.h> #ifdef CONFIG_MARCH_G5 /* * Function to divide an unsigned 64 bit integer by an unsigned * 31 bit integer using signed 64/32 bit division. */ static uint32_t __div64_31(uint64_t *n, uint32_t base) { register uint32_t reg2 asm("2"); register uint32_t reg3 asm("3"); uint32_t *words = (uint32_t *) n; uint32_t tmp; /* Special case base==1, remainder = 0, quotient = n */ if (base == 1) return 0; /* * Special case base==0 will cause a fixed point divide exception * on the dr instruction and may not happen anyway. For the * following calculation we can assume base > 1. The first * signed 64 / 32 bit division with an upper half of 0 will * give the correct upper half of the 64 bit quotient. */ reg2 = 0UL; reg3 = words[0]; asm volatile( " dr %0,%2\n" : "+d" (reg2), "+d" (reg3) : "d" (base) : "cc" ); words[0] = reg3; reg3 = words[1]; /* * To get the lower half of the 64 bit quotient and the 32 bit * remainder we have to use a little trick. Since we only have * a signed division the quotient can get too big. To avoid this * the 64 bit dividend is halved, then the signed division will * work. Afterwards the quotient and the remainder are doubled. * If the last bit of the dividend has been one the remainder * is increased by one then checked against the base. If the * remainder has overflown subtract base and increase the * quotient. Simple, no ? */ asm volatile( " nr %2,%1\n" " srdl %0,1\n" " dr %0,%3\n" " alr %0,%0\n" " alr %1,%1\n" " alr %0,%2\n" " clr %0,%3\n" " jl 0f\n" " slr %0,%3\n" " alr %1,%2\n" "0:\n" : "+d" (reg2), "+d" (reg3), "=d" (tmp) : "d" (base), "2" (1UL) : "cc" ); words[1] = reg3; return reg2; } /* * Function to divide an unsigned 64 bit integer by an unsigned * 32 bit integer using the unsigned 64/31 bit division. */ uint32_t __div64_32(uint64_t *n, uint32_t base) { uint32_t r; /* * If the most significant bit of base is set, divide n by * (base/2). That allows to use 64/31 bit division and gives a * good approximation of the result: n = (base/2)*q + r. The * result needs to be corrected with two simple transformations. * If base is already < 2^31-1 __div64_31 can be used directly. */ r = __div64_31(n, ((signed) base < 0) ? (base/2) : base); if ((signed) base < 0) { uint64_t q = *n; /* * First transformation: * n = (base/2)*q + r * = ((base/2)*2)*(q/2) + ((q&1) ? (base/2) : 0) + r * Since r < (base/2), r + (base/2) < base. * With q1 = (q/2) and r1 = r + ((q&1) ? (base/2) : 0) * n = ((base/2)*2)*q1 + r1 with r1 < base. */ if (q & 1) r += base/2; q >>= 1; /* * Second transformation. ((base/2)*2) could have lost the * last bit. * n = ((base/2)*2)*q1 + r1 * = base*q1 - ((base&1) ? q1 : 0) + r1 */ if (base & 1) { int64_t rx = r - q; /* * base is >= 2^31. The worst case for the while * loop is n=2^64-1 base=2^31+1. That gives a * maximum for q=(2^64-1)/2^31 = 0x1ffffffff. Since * base >= 2^31 the loop is finished after a maximum * of three iterations. */ while (rx < 0) { rx += base; q--; } r = rx; } *n = q; } return r; } #else /* MARCH_G5 */ uint32_t __div64_32(uint64_t *n, uint32_t base) { register uint32_t reg2 asm("2"); register uint32_t reg3 asm("3"); uint32_t *words = (uint32_t *) n; reg2 = 0UL; reg3 = words[0]; asm volatile( " dlr %0,%2\n" : "+d" (reg2), "+d" (reg3) : "d" (base) : "cc" ); words[0] = reg3; reg3 = words[1]; asm volatile( " dlr %0,%2\n" : "+d" (reg2), "+d" (reg3) : "d" (base) : "cc" ); words[1] = reg3; return reg2; } #endif /* MARCH_G5 */

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