I actually rewrote mulsf() in order to make it bit faster.
please check.
~d
On Friday 01 August 2003 21:47, Takahashi, Chris wrote:
> I noticed that the multiply function in libfp had a bug where you could not
> get negative numbers as results (e.g. 46.0 * -21.0 = 966). Upon examining
> mulsf.c it was discovered that the inline asm was not generating the
> expected asm (or at least the intended asm). The erroneous asm is below.
> As you can see at lines 117-119 r12 is erroneously being used as both %0
> and %B3. I'm not too good with inline assembly so I don't know if this is
> incorrect code or a compiler mistake. I also noticed lines 83-87 are
> inefficient and can be redone with a mov, xor, then and. This change alone
> didn't change fact that code was being generated contrary to intent.
>
> I found that changing a1 and a2 from type "r" to type "m" fixed this
> problem. I noticed that in the assembly code generated a1 and a2 ended up
> on the stack and needed to be moved to registers when inline was done so
> changing a1 and a2 to type "m" made since.
>
> Attached is the diff file (old - new +) with my fixes. Also attached is a
> .c file that illustrates this problem. Below I've pasted the diff.
>
> -Chris Takahashi
>
> ASM LIST:
> 81:mulsf.old.c **** /* sign = SIGN (fl1.l) ^ SIGN (fl2.l); */
> 82:mulsf.old.c **** __asm__ __volatile__ (
> 111 .LM9:
> 112 005a 2D41 mov @r1, r13
> 113 005c 1E41 0200 mov 2(r1), r14
> 114 0060 1B41 0400 mov 4(r1), r11
> 115 0064 1C41 0600 mov 4+2(r1), r12
> 116 /* #APP */
> 117 0068 0C4E mov r14, r12
> 118 006a 3CF0 0080 and #0x8000, r12
> 119 006e 0F4C mov r12, r15
> 120 0070 3FF0 0080 and #0x8000, r15
> 121 0074 0CEF xor r15, r12
> 122 /* #NOAPP */
> 123 0076 814C 0800 mov r12, 8(r1)
> 83:mulsf.old.c **** "mov %B2, %0 \n\t"
> 84:mulsf.old.c **** "and #0x8000, %0 \n\t"
> 85:mulsf.old.c **** "mov %B3, %1 \n\t"
> 86:mulsf.old.c **** "and #0x8000, %1 \n\t"
> 87:mulsf.old.c **** "xor %1, %0"
> 88:mulsf.old.c **** : "=r" (sign)
> 89:mulsf.old.c **** : "r" (tmp),
> 90:mulsf.old.c **** "r" (a1),
> 91:mulsf.old.c **** "r" (a2)
> 92:mulsf.old.c **** );
>
>
> FIX: (diff -u old new)
> --- msp430-libc/src/libm/mulsf.old.c 2003-08-01 08:55:47.000000000 -0700
> +++ msp430-libc/src/libm/mulsf.c 2003-08-01 10:18:02.000000000 -0700
> @@ -80,15 +80,12 @@
>
> /* sign = SIGN (fl1.l) ^ SIGN (fl2.l); */
> __asm__ __volatile__ (
> - "mov %B2, %0 \n\t"
> + "mov %B1, %0 \n\t"
> + "xor %B2, %0 \n\t"
> "and #0x8000, %0 \n\t"
> - "mov %B3, %1 \n\t"
> - "and #0x8000, %1 \n\t"
> - "xor %1, %0"
>
> : "=r" (sign)
>
> - : "r" (tmp),
> - "r" (a1),
> - "r" (a2)
> + : "m" (a1),
> + "m" (a2)
> );
>
> a1 = MANT (a1);
--
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