Re: [avr-gcc-list] Re: C vs. assembly performance

[Vincent Trouilliez]

On Sat, 28 Feb 2009 19:24:38 -0700
"Weddington, Eric" <address@hidden> wrote:
> You wouldn't need *nested* ifs, but an if-else-if structure, or better yet, a 
> table of function pointers, also known as a dispatch table. Each method 
> depends on the type of data that you're switching on.

I switch on an unsigned byte, with contiguous values (0-24).
A Function table sounds elegant to my ear, but it would mean 25
functions ! In my case the work is done in-situ, within the switch
statement, as it's takes only 2 or 3 statements to process a givne
"case". Using functions would be both overkill and overwhelming to
manage I think !! ;-)

I pasted my switch statement below for the curious.


--
Vince



void var_format(char *buff, uint8_t var_num)
{
uint16_t tmp16;
uint32_t tmp32;
int16_t tmpS16;

char Yes[] =            "  Yes";
char No[] =                     "   No";
char Unknown[] =        "-\?\?\?-";

        switch (var_num)
        {
                case ECU_COOLANT: 
                {// (N * 0.75) - 40             DB41                            
-40 to +150 °C
                        tmpS16 = (int16_t)(KLineFrameM1[41]) * 3 / 4 - 40;
                        var_format_S16(buff, tmpS16, 0);
                        break;
                }
                case ECU_ENGINE_SPEED: 
                {// MSB:LSB                                     DB12:13         
0 to 9999       RPM
                        ATOMIC_BLOCK(ATOMIC_FORCEON)
                        {
                                tmp16 = ((uint16_t)KLineFrameM1[12] << 8) + 
(uint16_t)KLineFrameM1[13];
                        }
                        var_format_S16(buff, (int16_t)tmp16, 0);
                        break;
                }
                case ECU_ROAD_SPEED: 
                {// DB14                                uint8_t MPH
                        var_format_byte(buff, KLineFrameM1[8]);
                        break;
                }
                case ECU_BARO_AIR_PRESSURE: 
                {// ((N-128)/100)+1             DB24                            
-0.28 to +2.27 Bar
                        tmpS16 = (int16_t)(KLineFrameM1[24]) - 28;
                        var_format_S16(buff, tmpS16, 2);
                        break;
                }
                case ECU_MAP_PRESSURE: 
                {// ((N-130)/100)+1      DB25                           -0.30 
to +2.25 Bar
                        tmpS16 = (int16_t)(KLineFrameM1[25]) - 30;
                        var_format_S16(buff, tmpS16, 2);
                        break;
                }
                case ECU_MAT_TEMP: 
                {// (N * 0.75) - 40             DB42                            
-40 to +150 °C
                        tmpS16 = (int16_t)(KLineFrameM1[42]) * 3 / 4 - 40;
                        var_format_S16(buff, tmpS16, 0);
                        break;
                }
                case ECU_THROTTLE_POSITION: 
                {// N / 2.55                                    DB27            
                0 to 100 %
                        tmp16 = (uint16_t)KLineFrameM1[27] * 100 / 255;
                        var_format_byte(buff, (uint8_t)tmp16);
                        break;
                }
                case ECU_ENGINE_LOAD: 
                {// DB36                                0 - 100 %
                        var_format_byte(buff, KLineFrameM1[36]);
                        break;
                }
                case ECU_KNOCK_COUNT: 
                {// DB43                                uint8_t
                        var_format_byte(buff, KLineFrameM1[43]);
                        break;
                }
                case ECU_KNOCK_RETARD: 
                {// (N * 45) / 255                      DB44                    
        0 to 45 Deg
                        tmp16 = (uint16_t)KLineFrameM1[44] * 90 / 51;
                        var_format_S16(buff, (int16_t)tmp16, 1);
                        break;
                }
                case ECU_SPARK_ADVANCE: 
                {// (N * 9000)/256   MSB:LSB       DB39:40        0.00 Degrees
                        ATOMIC_BLOCK(ATOMIC_FORCEON)
                        {
                                tmp16 = ((uint16_t)KLineFrameM1[39] << 8) + 
(uint16_t)KLineFrameM1[40];
                        }
                        tmp32 = (uint32_t)tmp16 * 9000 / 256;
                        var_format_S16(buff, (int16_t)tmp32, 2);
                        break;
                }
                case ECU_BOOST_DC: 
                {// DB31                                uint8_t or %, don't know
                        var_format_byte(buff, KLineFrameM1[31]);
                        break;
                }
                case ECU_MAIN_INJ_DC: 
                {// DB45                                uint8_t
                        var_format_byte(buff, KLineFrameM1[45]);
                        break;
                }
                case ECU_SECONDARY_INJ_DC: 
                {// DB37                                uint8_t
                        var_format_byte(buff, KLineFrameM1[37]);
                        break;
                }
                case ECU_AF_RATIO: 
                {// N * 10                                      DB47            
                0.0 to 25.5
                        var_format_S16(buff, (int16_t)KLineFrameM1[47], 1);
                        break;
                }
                case ECU_IAC_POSITION: 
                {// DB23                                0 to 170
                        var_format_byte(buff, KLineFrameM1[23]);
                        break;
                }
                case ECU_COOLANT_START: 
                {// (N * 0.75) - 40             DB9            -40 to +150 °C
                        tmpS16 = (int16_t)(KLineFrameM1[9]) * 3 / 4 - 40;
                        var_format_S16(buff, tmpS16, 0);
                        break;
                }
                case ECU_DESIRED_IDLE: 
                {// N * 12.5                                    DB11            
                0 to 3187       RPM
                        tmp16 = (uint16_t)(KLineFrameM1[11]) * 25 / 2;
                        var_format_S16(buff, (int16_t)tmp16, 0);
                        break;
                }
                case ECU_RAW_ADC_COOLANT: 
                {// DB8                         uint8_t
                        var_format_byte(buff, KLineFrameM1[8]);
                        break;
                }
                case ECU_RAW_ADC_THROTTLE: 
                {// DB10                                uint8_t
                        var_format_byte(buff, KLineFrameM1[10]);
                        break;
                }
                case ECU_RAW_ADC_MAT: 
                {// DB29                                uint8_t
                        var_format_byte(buff, KLineFrameM1[29]);
                        break;
                }
                case ECU_CLOSED_LOOP_MODE: 
                {// DB63 & 0x80         YES/NO
                        if ( KLineFrameM1[63] & 0x80 )
                                strcpy(buff, Yes);
                        else
                                strcpy(buff, No);
                        break;
                }
                case ECU_AIR_CON_DEMAND: 
                {// DB6 & 0x08          YES/NO
                        if ( KLineFrameM1[6] & 0x08 )
                                strcpy(buff, Yes);
                        else
                                strcpy(buff, No);
                        break;
                }
                case ECU_AIR_CON_ENGAGED: 
                {// DB7 & 0x01          YES/NO
                        if ( KLineFrameM1[7] & 0x01 )
                                strcpy(buff, Yes);
                        else
                                strcpy(buff, No);
                        break;
                }
                case ECU_FAN_RUNNING: 
                {// DB7 & 0x04          YES/NO
                        if ( KLineFrameM1[7] & 0x04 )
                                strcpy(buff, Yes);
                        else
                                strcpy(buff, No);
                        break;
                }
                default:
                        strcpy(buff, Unknown);
        }

}