/*
 * Copyright (c) 2010 Broadcom Corporation
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include "phy_qmath.h"

/*
 * Description: This function make 16 bit unsigned multiplication.
 * To fit the output into 16 bits the 32 bit multiplication result is right
 * shifted by 16 bits.
 */
u16 qm_mulu16(u16 op1, u16 op2)
{
        return (u16) (((u32) op1 * (u32) op2) >> 16);
}

/*
 * Description: This function make 16 bit multiplication and return the result
 * in 16 bits. To fit the multiplication result into 16 bits the multiplication
 * result is right shifted by 15 bits. Right shifting 15 bits instead of 16 bits
 * is done to remove the extra sign bit formed due to the multiplication.
 * When both the 16bit inputs are 0x8000 then the output is saturated to
 * 0x7fffffff.
 */
s16 qm_muls16(s16 op1, s16 op2)
{
        s32 result;
        if (op1 == (s16) 0x8000 && op2 == (s16) 0x8000)
                result = 0x7fffffff;
        else
                result = ((s32) (op1) * (s32) (op2));

        return (s16) (result >> 15);
}

/*
 * Description: This function add two 32 bit numbers and return the 32bit
 * result. If the result overflow 32 bits, the output will be saturated to
 * 32bits.
 */
s32 qm_add32(s32 op1, s32 op2)
{
        s32 result;
        result = op1 + op2;
        if (op1 < 0 && op2 < 0 && result > 0)
                result = 0x80000000;
        else if (op1 > 0 && op2 > 0 && result < 0)
                result = 0x7fffffff;

        return result;
}

/*
 * Description: This function add two 16 bit numbers and return the 16bit
 * result. If the result overflow 16 bits, the output will be saturated to
 * 16bits.
 */
s16 qm_add16(s16 op1, s16 op2)
{
        s16 result;
        s32 temp = (s32) op1 + (s32) op2;
        if (temp > (s32) 0x7fff)
                result = (s16) 0x7fff;
        else if (temp < (s32) 0xffff8000)
                result = (s16) 0xffff8000;
        else
                result = (s16) temp;

        return result;
}

/*
 * Description: This function make 16 bit subtraction and return the 16bit
 * result. If the result overflow 16 bits, the output will be saturated to
 * 16bits.
 */
s16 qm_sub16(s16 op1, s16 op2)
{
        s16 result;
        s32 temp = (s32) op1 - (s32) op2;
        if (temp > (s32) 0x7fff)
                result = (s16) 0x7fff;
        else if (temp < (s32) 0xffff8000)
                result = (s16) 0xffff8000;
        else
                result = (s16) temp;

        return result;
}

/*
 * Description: This function make a 32 bit saturated left shift when the
 * specified shift is +ve. This function will make a 32 bit right shift when
 * the specified shift is -ve. This function return the result after shifting
 * operation.
 */
s32 qm_shl32(s32 op, int shift)
{
        int i;
        s32 result;
        result = op;
        if (shift > 31)
                shift = 31;
        else if (shift < -31)
                shift = -31;
        if (shift >= 0) {
                for (i = 0; i < shift; i++)
                        result = qm_add32(result, result);
        } else {
                result = result >> (-shift);
        }

        return result;
}

/*
 * Description: This function make a 16 bit saturated left shift when the
 * specified shift is +ve. This function will make a 16 bit right shift when
 * the specified shift is -ve. This function return the result after shifting
 * operation.
 */
s16 qm_shl16(s16 op, int shift)
{
        int i;
        s16 result;
        result = op;
        if (shift > 15)
                shift = 15;
        else if (shift < -15)
                shift = -15;
        if (shift > 0) {
                for (i = 0; i < shift; i++)
                        result = qm_add16(result, result);
        } else {
                result = result >> (-shift);
        }

        return result;
}

/*
 * Description: This function make a 16 bit right shift when shift is +ve.
 * This function make a 16 bit saturated left shift when shift is -ve. This
 * function return the result of the shift operation.
 */
s16 qm_shr16(s16 op, int shift)
{
        return qm_shl16(op, -shift);
}

/*
 * Description: This function return the number of redundant sign bits in a
 * 32 bit number. Example: qm_norm32(0x00000080) = 23
 */
s16 qm_norm32(s32 op)
{
        u16 u16extraSignBits;
        if (op == 0) {
                return 31;
        } else {
                u16extraSignBits = 0;
                while ((op >> 31) == (op >> 30)) {
                        u16extraSignBits++;
                        op = op << 1;
                }
        }
        return u16extraSignBits;
}

/* This table is log2(1+(i/32)) where i=[0:1:31], in q.15 format */
static const s16 log_table[] = {
        0,
        1455,
        2866,
        4236,
        5568,
        6863,
        8124,
        9352,
        10549,
        11716,
        12855,
        13968,
        15055,
        16117,
        17156,
        18173,
        19168,
        20143,
        21098,
        22034,
        22952,
        23852,
        24736,
        25604,
        26455,
        27292,
        28114,
        28922,
        29717,
        30498,
        31267,
        32024
};

#define LOG_TABLE_SIZE 32       /* log_table size */
#define LOG2_LOG_TABLE_SIZE 5   /* log2(log_table size) */
#define Q_LOG_TABLE 15          /* qformat of log_table */
#define LOG10_2         19728   /* log10(2) in q.16 */

/*
 * Description:
 * This routine takes the input number N and its q format qN and compute
 * the log10(N). This routine first normalizes the input no N.  Then N is in
 * mag*(2^x) format. mag is any number in the range 2^30-(2^31 - 1).
 * Then log2(mag * 2^x) = log2(mag) + x is computed. From that
 * log10(mag * 2^x) = log2(mag * 2^x) * log10(2) is computed.
 * This routine looks the log2 value in the table considering
 * LOG2_LOG_TABLE_SIZE+1 MSBs. As the MSB is always 1, only next
 * LOG2_OF_LOG_TABLE_SIZE MSBs are used for table lookup. Next 16 MSBs are used
 * for interpolation.
 * Inputs:
 * N - number to which log10 has to be found.
 * qN - q format of N
 * log10N - address where log10(N) will be written.
 * qLog10N - address where log10N qformat will be written.
 * Note/Problem:
 * For accurate results input should be in normalized or near normalized form.
 */
void qm_log10(s32 N, s16 qN, s16 *log10N, s16 *qLog10N)
{
        s16 s16norm, s16tableIndex, s16errorApproximation;
        u16 u16offset;
        s32 s32log;

        /* normalize the N. */
        s16norm = qm_norm32(N);
        N = N << s16norm;

        /* The qformat of N after normalization.
         * -30 is added to treat the no as between 1.0 to 2.0
         * i.e. after adding the -30 to the qformat the decimal point will be
         * just rigtht of the MSB. (i.e. after sign bit and 1st MSB). i.e.
         * at the right side of 30th bit.
         */
        qN = qN + s16norm - 30;

        /* take the table index as the LOG2_OF_LOG_TABLE_SIZE bits right of the
         * MSB */
        s16tableIndex = (s16) (N >> (32 - (2 + LOG2_LOG_TABLE_SIZE)));

        /* remove the MSB. the MSB is always 1 after normalization. */
        s16tableIndex =
                s16tableIndex & (s16) ((1 << LOG2_LOG_TABLE_SIZE) - 1);

        /* remove the (1+LOG2_OF_LOG_TABLE_SIZE) MSBs in the N. */
        N = N & ((1 << (32 - (2 + LOG2_LOG_TABLE_SIZE))) - 1);

        /* take the offset as the 16 MSBS after table index.
         */
        u16offset = (u16) (N >> (32 - (2 + LOG2_LOG_TABLE_SIZE + 16)));

        /* look the log value in the table. */
        s32log = log_table[s16tableIndex];      /* q.15 format */

        /* interpolate using the offset. q.15 format. */
        s16errorApproximation = (s16) qm_mulu16(u16offset,
                                (u16) (log_table[s16tableIndex + 1] -
                                       log_table[s16tableIndex]));

         /* q.15 format */
        s32log = qm_add16((s16) s32log, s16errorApproximation);

        /* adjust for the qformat of the N as
         * log2(mag * 2^x) = log2(mag) + x
         */
        s32log = qm_add32(s32log, ((s32) -qN) << 15);   /* q.15 format */

        /* normalize the result. */
        s16norm = qm_norm32(s32log);

        /* bring all the important bits into lower 16 bits */
        /* q.15+s16norm-16 format */
        s32log = qm_shl32(s32log, s16norm - 16);

        /* compute the log10(N) by multiplying log2(N) with log10(2).
         * as log10(mag * 2^x) = log2(mag * 2^x) * log10(2)
         * log10N in q.15+s16norm-16+1 (LOG10_2 is in q.16)
         */
        *log10N = qm_muls16((s16) s32log, (s16) LOG10_2);

        /* write the q format of the result. */
        *qLog10N = 15 + s16norm - 16 + 1;

        return;
}