path: root/pk/ppe42/ppe42_gcc.c

//-----------------------------------------------------------------------------
// *! (C) Copyright International Business Machines Corp. 2014
// *! All Rights Reserved -- Property of IBM
// *! *** IBM Confidential ***
//-----------------------------------------------------------------------------

/// \file ppe42_gcc.h
/// \brief 32-bit PowerPC functions expected by GCC
///
/// GCC expects certain built-in functions to be defined in the environment.
/// Since PK applications are statically linked, we must define these
/// functions ourselves to avoid a static link with the GCC libraries, which
/// would legaly require us to distribute (at least) the binary forms of PK
/// applications.
///
/// We obviously had to look at some GCC library code to understand the
/// specifications of these routines.  However, all of the code here is new -
/// no structure definitions or lines of executable code were copied from the
/// GCC sources.

#include "pk.h"
#include "ppe42_gcc.h"

/// A 64-bit logical right shift.
///
/// Note that shifts with negative shift counts or shifts with shift counts
/// longer than 63 bits are undefined.

uint64_t
__lshrdi3(uint64_t x, int i)
{
    Uint64 input, result;

    if (i == 0) {
        return x;
    }

    input.value = x;

    if (i >= 32) {
        result.word[0] = 0;
        result.word[1] = input.word[0] >> (i - 32);
    } else {
        result.word[0] = input.word[0] >> i;
        result.word[1] = (input.word[1] >> i) | (input.word[0] << (32 - i));
    }

    return result.value;
}


/// A 64 bit arithmetic left shift.
///
/// Note that shifts with negative shift counts or shifts with shift counts
/// longer than 63 bits are undefined.

uint64_t
__ashldi3(uint64_t x, int i)
{
    Uint64 input, result;

    if (i == 0) {
        return x;
    }

    input.value = x;

    if (i >= 32) {
        result.word[1] = 0;
        result.word[0] = input.word[1] << (i - 32);
    } else {
        result.word[1] = input.word[1] << i;
        result.word[0] = (input.word[0] << i) | (input.word[1] >> (32 - i));
    }

    return result.value ;

}


/// A 64 bit arithmetic right shift.
///
/// Note that shifts with negative shift counts or shifts with shift counts
/// longer than 63 bits are undefined.

uint64_t
__ashrdi3(uint64_t x, int i)
{
    Int64 input, result;

    if (i == 0) {
        return x;
    }

    input.value = x;

    if (i >= 32) {
        result.word[0] = input.word[0] >> 31;
        result.word[1] = input.word[0] >> (i - 32);
    } else {
        result.word[0] = input.word[0] >> i;
        result.word[1] = 
            (((uint32_t)input.word[1]) >> i) | 
            (input.word[0] << (32 - i));
    }

    return result.value ;

}


/// 32-bit Population count

// This is a well-known divide-and-conquer algorithm, e.g. look on Wikipedia
// under "Hamming Weight". The idea is to compute sums of adjacent bit
// segments in parallel, in place. 

int
__popcountsi2(uint32_t x)
{
    uint32_t m1 = 0x55555555;
    uint32_t m2 = 0x33333333;
    uint32_t m4 = 0x0f0f0f0f;
    x -= (x >> 1) & m1;            /* Sum pairs of bits */
    x = (x & m2) + ((x >> 2) & m2);/* Sum 4-bit segments */
    x = (x + (x >> 4)) & m4;       /* Sum 8-bit segments */
    x += x >>  8;                  /* Sum 16-bit segments */
    return (x + (x >> 16)) & 0x3f; /* Final sum */
}


/// 64-bit Population count

int
__popcountdi2(uint64_t x)
{
    return __popcountsi2(x >> 32) + __popcountsi2(x & 0xffffffff);
}


// 64-bit divides
//
// For the unsigned case, note that divide by 0 returns quotient = remainder =
// 0. 
//
// For the signed case, in general we perform the division on the absolute
// values and fix the signs of the quotient and remainder at the end.
//
// For the signed case, the convention in other libraries seems to be to
// ignore the case of the most-negative integer.  Although it seems "wrong" to
// return the wrong answer when the right answer can be easily computed, in
// the interest of code size we follow the convention here and ignore the most
// negative integer.
//
// The assembler routine __ppe42_udiv64() assembles to ??? bytes.  The full C
// routine __ppc_sdiv64 compiles to ??? bytes with the most-negative checks,
// but only ??? bytes as configured here.

// For the signed cases, we need to handle the special case that the dividend
// or divisor is the most negative integer.  
//
// If the dividend is the most negative integer, then dividing this integer by
// -1 would overflow as a positive quotient, so we set quotient and remainder
// to 0 in this case.  For divide by 1, the quotient is the most negative
// integer. Otherwise we adjust the dividend by the absolute value of the
// divisor, then fix up the quotient later by adding or subtracting 1.
//
// If the divisor is the most negative integer, then the quotient is always 0
// unless the dividend is also the most negative integer, in which case the
// quotient is 1 and the remainder is 0.
//

uint64_t 
__udivdi3(uint64_t u, uint64_t v)
{
    uint64_t quotient, remainder;

    __ppe42_udiv64(u, v, &quotient, &remainder);
    return quotient;
}


uint64_t 
__umoddi3(uint64_t u, uint64_t v)
{
    uint64_t quotient, remainder;

    __ppe42_udiv64(u, v, &quotient, &remainder);
    return remainder;
}


#if 0
#define INT64_T_MIN ((int64_t)(0x8000000000000000ull))
#endif

void
__ppe42_sdiv64(int64_t u, int64_t v, 
               int64_t *quotient, int64_t *remainder)
{
    int q_negate, r_negate;
    uint64_t uu, uv;
#if 0
    int fixup = 0;
#endif

    q_negate = (u < 0) ^ (v < 0);
    r_negate = (u < 0);
    uu = (u < 0 ? -u : u);
    uv = (v < 0 ? -v : v);

#if 0
    if (u == INT64_T_MIN) {
        if (v == -1) {
            *quotient = 0;
            *remainder = 0;
            return;
        } else if (v == 1) {
            *quotient = INT64_T_MIN;
            *remainder = 0;
            return;
        } else if (v == INT64_T_MIN) {
            *quotient = 1;
            *remainder = 0;
            return;
        } else {
            fixup = 1;
            u += (v < 0 ? -v : v);
        }
    } else if (v == INT64_T_MIN) {
        *quotient = 0;
        *remainder = u;
        return;
    }
#endif

    __ppe42_udiv64(uu, uv, (uint64_t *)quotient, (uint64_t *)remainder);

#if 0
    if (fixup) {
        *quotient += 1;
    }
#endif
    if (q_negate) {
        *quotient = -(*quotient);
    }
    if (r_negate) {
        *remainder = -(*remainder);
    }
}
            

int64_t  
__divdi3(int64_t u, int64_t v)
{
    int64_t quotient, remainder;

    __ppe42_sdiv64(u, v, &quotient, &remainder);
    return quotient;
}


int64_t  
__moddi3(int64_t u, int64_t v)
{
    int64_t quotient, remainder;

    __ppe42_sdiv64(u, v, &quotient, &remainder);
    return remainder;
}


/// 64-bit unsigned compare as a function, returning 0 (<), 1 (==) or 2 (>).

int
__ucmpdi2(uint64_t i_a, uint64_t i_b)
{
    Uint64 a, b;
    int rv;

    a.value = i_a;
    b.value = i_b;

    if (a.word[0] < b.word[0]) {
        rv = 0;
    } else if (a.word[0] > b.word[0]) {
        rv = 2;
    } else if (a.word[1] < b.word[1]) {
        rv = 0;
    } else if (a.word[1] > b.word[1]) {
        rv = 2;
    } else {
        rv = 1;
    }

    return rv;
}