bits.qh

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#pragma once

#include "log.qh"

#define BIT(n) (1 << (n))
#define BITS(n) (BIT(n) - 1)
#ifndef BRANCHLESS_BITSET
    #define BITSET(var, mask, flag) (flag ? (var) | (mask) : (var) & ~(mask))
#else
    #define BITSET(var, mask, flag) ((var) ^ (-(flag) ^ (var)) & (mask))
#endif

ERASEABLE
int lowestbit(int f)
{
    f &= ~(f << 1);
    f &= ~(f << 2);
    f &= ~(f << 4);
    f &= ~(f << 8);
    f &= ~(f << 16);
    return f;
}

ERASEABLE
int randombit(int bits)
{
    if (!(bits & (bits - 1)))  // this ONLY holds for powers of two!
        return bits;

    int r = random();
    int b = 0;
    int n = 0;

    for (int f = 1; f <= bits; f *= 2)
    {
        if (bits & f)
        {
            ++n;
            r *= n;
            if (r <= 1) b = f;
            else r = (r - 1) / (n - 1);
        }
    }
    return b;
}

ERASEABLE
int randombits(int bits, int k, bool error_return)
{
    int r = 0;
    while (k > 0 && bits != r)
    {
        r += randombit(bits - r);
        --k;
    }
    if (error_return)
        if (k > 0) return -1;
    // all
    return r;
}

/*
void randombit_test(int bits, int iter)
{
    while (iter > 0)
    {
        LOG_INFO(ftos(randombit(bits)), "\n");
        --iter;
    }
}
*/

enum {
    OP_SET,
    OP_MIN,
    OP_MAX,
    OP_PLUS,
    OP_MINUS
};

ERASEABLE
bool GiveBit(entity e, .int fld, int bit, int op, int val)
{
    int v0 = (e.(fld) & bit);
    switch (op)
    {
        case OP_SET:
            if (val > 0) e.(fld) |= bit;
            else e.(fld) &= ~bit;
            break;
        case OP_MIN:
        case OP_PLUS:
            if (val > 0) e.(fld) |= bit;
            break;
        case OP_MAX:
            if (val <= 0) e.(fld) &= ~bit;
            break;
        case OP_MINUS:
            if (val > 0) e.(fld) &= ~bit;
            break;
    }
    int v1 = (e.(fld) & bit);
    return v0 != v1;
}

ERASEABLE
bool GiveValue(entity e, .int fld, int op, int val)
{
    int v0 = e.(fld);
    switch (op)
    {
        case OP_SET:
            e.(fld) = val;
            break;
        case OP_MIN:
            e.(fld) = max(e.(fld), val);  // min 100 cells = at least 100 cells
            break;
        case OP_MAX:
            e.(fld) = min(e.(fld), val);
            break;
        case OP_PLUS:
            e.(fld) += val;
            break;
        case OP_MINUS:
            e.(fld) -= val;
            break;
    }
    int v1 = e.(fld);
    return v0 != v1;
}