1 files changed, 74 insertions, 0 deletions
diff --git a/libc/i386fp/ldexp.x b/libc/i386fp/ldexp.x
new file mode 100644
index 0000000..bc9dd03
--- /dev/null
+++ b/libc/i386fp/ldexp.x
@@ -0,0 +1,74 @@
+! bcc 386 floating point routines (version 2) -- _ldexp
+! authors: Timothy Murphy (tim@maths.tcd.ie), Bruce Evans
+
+#include "fplib.h"
+
+	.extern	fpoverflow
+	.extern	fpunderflow
+
+! void ldexp(double value, int exponent);
+! returns value * (2 ** exponent)
+
+	.globl	_ldexp
+	.align	ALIGNMENT
+_ldexp:
+push ebx
+#undef PC_SIZE
+#define PC_SIZE 8
+	mov	ebx,PC_SIZE+D_HIGH[esp]	! upper dword of x
+	mov	ecx,PC_SIZE+D_SIZE[esp]	! exponent arg
+	mov	eax,ebx		! extract exponent (of x) here
+	and	eax,#D_EXP_MASK
+!	jz	exp_y_0		! may need check for preposterous exponent arg too
+
+	shr	eax,#D_EXP_SHIFT	! shift to low bits just for testing
+	jz	underflow	! denormal?
+	add	eax,ecx		! test-add the exponents
+	jz	underflow	! XXX probably need to fiddle norm bit
+	cmp	eax,#D_EXP_INFINITE	! check if still within range
+	jae	outofbounds	! the unsigned compare catches all overflow cases
+				! because the exponent of x is non-negative
+
+	shl	ecx,#D_EXP_SHIFT	! shift exponent arg bits into final position ...
+	add	ebx,ecx		! ... safe to add it to exponent of x now
+	mov	eax,PC_SIZE+D_LOW[esp]	! lower dword of x
+mov edx,ebx
+pop ebx
+	ret
+
+
+	.align	ALIGNMENT
+outofbounds:
+	test	ecx,ecx		! overflow or underflow?
+	jns	overflow
+underflow:
+	mov	edx,ebx		! put sign in usual reg
+	push	edi
+	push	esi
+	mov	edi,eax		! put exponent in usual reg
+	mov	eax,2*GENREG_SIZE+PC_SIZE+D_LOW[esp]
+				! put lower dword of x in usual reg
+	mov	esi,ebx		! put upper dword of x in usual reg
+	and	esi,#D_EXP_MASK | D_FRAC_MASK
+	test	esi,#D_EXP_MASK
+	jz	foo
+	and	esi,#D_FRAC_MASK
+	or	esi,#D_NORM_MASK
+foo:
+	neg	edi
+!	inc	edi		! XXX ?
+	call	fpunderflow
+	pop	esi
+	pop	edi
+	mov	ebx,edx		! XXX = wrong reg
+pop ebx
+	ret
+
+	.align	ALIGNMENT
+overflow:
+	mov	edx,ebx		! put sign in usual reg
+	call	fpoverflow
+	mov	eax,ecx		! XXX = wrong reg
+	mov	ebx,edx		! XXX = wrong reg
+pop ebx
+	ret