> But m2 should be 16-bit, and yet is generated as 8-bit.
you're right...
I'll fix it in a minute... (already in cvs. :)
> Incidently, is the inline multiply code faster than using the hardware
> multiply? I can see it would be for small constants, but do you switch
> over automatically for constants that generate larger code? Also, is it
Well. There is a threshold...
Probably this should be smaller a bit. Agree.
> not possible to optomise the 7 "rla" instructions as a "swapb" then an
> "rra" ?
You'll loose 1 bit then. I thought about it...
~d
>
> The command-line I used was this (although I also tried with optomisation
> off - it made no difference):
> msp430-gcc -c -mmcu=msp430x149 -g -O2 -fverbose-asm -Wa,-ahld=test.lst
> test.c
>
> mvh.
>
> David
>
>
> /**** test.c ****/
>
> #define scale 122
>
> unsigned int m1(unsigned char b) {
> // The mult is 8-bit
> return b*scale;
> }
>
> unsigned int m2(unsigned char b) {
> // The mult should be 16-bit, but is actually 8-bit
> return ((unsigned int)b) * scale;
> }
>
> unsigned int m3(unsigned int w) {
> // The mult is 16-bit
> return w * scale;
> }
>
> unsigned int m4(unsigned char b) {
> // The mult is 16-bit
> unsigned int w = b;
> return w * scale;
> }
>
>
> /**** test.lst ****/
>
> 12:test.c **** #define scale 122
> 13:test.c ****
> 14:test.c **** unsigned int m1(unsigned char b) {
> 109 .LM1:
> 110 /* prologue: frame size = 0 */
> 111 .L__FrameSize_m1=0x0
> GAS LISTING /cygdrive/d/temp/ccGc8q6D.s page 2
>
>
> 112 .L__FrameOffset_m1=0x0
> 113 /* prologue end (size=0) */
> 15:test.c **** // The mult is 8-bit
> 16:test.c **** return b*scale;
> 115 .LM2:
> 116 0000 4E4F mov.b r15, r14 ; b, b
> 117 0002 0E5E rla r14 ; b
> 118 0004 0E5E rla r14 ; b
> 119 0006 0E5E rla r14 ; b
> 120 0008 0E5E rla r14 ; b
> 121 000a 0E5E rla r14 ; b
> 122 000c 0E5E rla r14 ; b
> 123 000e 0E5E rla r14 ; b
> 124 0010 4F5F rla.b r15 ; b
> 125 0012 4E8F sub.b r15, r14 ; b, b
> 126 0014 4E8F sub.b r15, r14 ; b, b
> 127 0016 4E8F sub.b r15, r14 ; b, b
> 17:test.c **** }
> 129 .LM3:
> 130 0018 0F4E mov r14, r15 ; b
> 131 001a 3041 ret
> 132 /* epilogue: not required */
> 133 /* function m1 size 14 (13) */
> 134 .Lfe1:
> 136 /********* End of function ******/
> 137
> 138 .Lscope0:
> 140 .p2align 1,0
> 143 .global m2
> 145 /***********************
> 146 * Function `m2'
> 147 ***********************/
> 148 m2:
> 18:test.c ****
> 19:test.c **** unsigned int m2(unsigned char b) {
> 150 .LM4:
> 151 /* prologue: frame size = 0 */
> 152 .L__FrameSize_m2=0x0
> 153 .L__FrameOffset_m2=0x0
> 154 /* prologue end (size=0) */
> 20:test.c **** // The mult should be 16-bit, but is actually
> 8-bit 21:test.c **** return ((unsigned int)b) * scale;
> 156 .LM5:
> 157 001c 4E4F mov.b r15, r14 ; b, b
> 158 001e 0E5E rla r14 ; b
> 159 0020 0E5E rla r14 ; b
> 160 0022 0E5E rla r14 ; b
> 161 0024 0E5E rla r14 ; b
> 162 0026 0E5E rla r14 ; b
> 163 0028 0E5E rla r14 ; b
> 164 002a 0E5E rla r14 ; b
> 165 002c 4F5F rla.b r15 ; b
> 166 002e 4E8F sub.b r15, r14 ; b, b
> 167 0030 4E8F sub.b r15, r14 ; b, b
> 168 0032 4E8F sub.b r15, r14 ; b, b
> 22:test.c **** }
> 170 .LM6:
> GAS LISTING /cygdrive/d/temp/ccGc8q6D.s page 3
>
>
> 171 0034 0F4E mov r14, r15 ; b
> 172 0036 3041 ret
> 173 /* epilogue: not required */
> 174 /* function m2 size 14 (13) */
> 175 .Lfe2:
> 177 /********* End of function ******/
> 178
> 179 .Lscope1:
> 181 .p2align 1,0
> 184 .global m3
> 186 /***********************
> 187 * Function `m3'
> 188 ***********************/
> 189 m3:
> 23:test.c ****
> 24:test.c **** unsigned int m3(unsigned int w) {
> 191 .LM7:
> 192 /* prologue: frame size = 0 */
> 193 .L__FrameSize_m3=0x0
> 194 .L__FrameOffset_m3=0x0
> 195 /* prologue end (size=0) */
> 25:test.c **** // The mult is 16-bit
> 26:test.c **** return w * scale;
> 197 .LM8:
> 198 0038 0E4F mov r15, r14 ; w, w
> 199 003a 0E5E rla r14 ; w
> 200 003c 0E5E rla r14 ; w
> 201 003e 0E5E rla r14 ; w
> 202 0040 0E5E rla r14 ; w
> 203 0042 0E5E rla r14 ; w
> 204 0044 0E5E rla r14 ; w
> 205 0046 0E5E rla r14 ; w
> 206 0048 0F5F rla r15 ; w
> 207 004a 0E8F sub r15, r14 ; w, w
> 208 004c 0E8F sub r15, r14 ; w, w
> 209 004e 0E8F sub r15, r14 ; w, w
> 27:test.c **** }
> 211 .LM9:
> 212 0050 0F4E mov r14, r15 ; w
> 213 0052 3041 ret
> 214 /* epilogue: not required */
> 215 /* function m3 size 14 (13) */
> 216 .Lfe3:
> 218 /********* End of function ******/
> 219
> 220 .Lscope2:
> 222 .p2align 1,0
> 225 .global m4
> 227 /***********************
> 228 * Function `m4'
> 229 ***********************/
> 230 m4:
> 28:test.c ****
> 29:test.c **** unsigned int m4(unsigned char b) {
> 232 .LM10:
> 233 /* prologue: frame size = 0 */
> 234 .L__FrameSize_m4=0x0
> GAS LISTING /cygdrive/d/temp/ccGc8q6D.s page 4
>
>
> 235 .L__FrameOffset_m4=0x0
> 236 /* prologue end (size=0) */
> 237 .LBB2:
> 30:test.c **** // The mult is 16-bit
> 31:test.c **** unsigned int w = b;
> 239 .LM11:
> 240 0054 4E4F mov.b r15, r14 ; b, w
> 32:test.c **** return w * scale;
> 242 .LM12:
> 243 0056 0F4E mov r14, r15 ; w, w
> 244 0058 0F5F rla r15 ; w
> 245 005a 0F5F rla r15 ; w
> 246 005c 0F5F rla r15 ; w
> 247 005e 0F5F rla r15 ; w
> 248 0060 0F5F rla r15 ; w
> 249 0062 0F5F rla r15 ; w
> 250 0064 0F5F rla r15 ; w
> 251 0066 0E5E rla r14 ; w
> 252 0068 0F8E sub r14, r15 ; w, w
> 253 006a 0F8E sub r14, r15 ; w, w
> 254 006c 0F8E sub r14, r15 ; w, w
> 255 .LBE2:
> 33:test.c **** }
> 257 .LM13:
> 258 006e 3041 ret
> 259 /* epilogue: not required */
> 260 /* function m4 size 14 (13) */
> 261 .Lfe4:
> 263 /********* End of function ******/
> 264
>
>
>
>
>
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